Roasted Mushroom Sandwich with Horseradish Aioli Recipe - Savory Sojourn
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Roasted Mushroom Sandwich with Horseradish Aioli

19 reviews / 4.8 average

Layers of roasty mushrooms, havarti, lemony arugula, and an easy homemade horseradish aioli make this mushroom sandwich a WINNER. A saucy, salty, hefty masterpiece!

The Mushroom Sandwich That I Can’t Quit

Do I always talk about Ang or do I always talk about Ang?

Really, all my favorite food ideas come from Ang. Texas style chili, chicken wraps, and the famous tortellini soup.

I got a text a few weeks ago from Ang with a photo of her sandwich – like friends do – which was layers of roast beef, arugula, havarti, and horseradish aioli on the caramelized onion focaccia from Trader Joe’s. I spent at least 10 minutes just zoomed in on the photo, examining every saucy detail. Then I went and immediately made one for myself.

I was feeling called to a no-beef-but-still-beefy mushroom version, and it is beyond.

That horseradish aioli is pulled from the old fave portobello French dip recipe (5 star, so good), and the roasty mushrooms, havarti, and arugula create layers of flavor that were just meant to be together. It might be over the top, but I also like a shmear of pesto rosso on the bottom of the focaccia so you can get a little tomatoey brightness in the mix.

Please go sink your teeth into this smushy, saucy, salty and hefty masterpiece. It is a good one.

How To Make This Mushroom Sandwich


Roast the mushrooms.

Toss the mushrooms with olive oil and a hefty sprinkle of seasoning (I use Cajun seasoning). Roast ’em up till they’re golden, chewy, and delicious.

Hands mixing sliced mushrooms with oil and spices.


Make that horseradish sauce.

Oh man, it’s so good. Mix your mayo, garlic, lemon, and horseradish together. Season with salt.

Mixing aioli in a bowl with mayonnaise, horseradish, garlic, and lemon juice.


Toast and split the bread.

Would highly recommend the caramelized onion focaccia from Trader Joe’s for this one.

Slicing focaccia on a cutting board.


Layer your sandwich.

My layers: pesto rosso (also from Trader Joe’s, and optional), mushrooms, havarti cheese (melted for funs), arugula, and horseradish sauce on top.

Placing arugula on a mushroom sandwich.


You’re Done! Yum.

Devour and enjoy.

Mushroom sandwich cut in half and opened.

Watch How To Make This Mushroom Sandwich

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A picture of Roasted Mushroom Sandwich with Horseradish Aioli

Roasted Mushroom Sandwich with Horseradish Aioli

  • Author: Lindsay Ostrom
  • Total Time: 40 minutes
  • Yield: this makes enough mushrooms and sauce for 3-4 sandwiches


Layers of roasty mushrooms, havarti, lemony arugula, and an easy homemade horseradish aioli make this mushroom sandwich a WINNER. A saucy, salty, hefty masterpiece!


Units Scale

Roasted Mushrooms

  • 16 ounces sliced mushrooms (portobello or white button mushrooms)
  • 2 tablespoons avocado oil
  • 2 tablespoons Cajun seasoning (if it has salt in it, you may want to add less of it just to make sure the mushrooms don’t get too salty – every brand is different)
  • salt and pepper to taste

Horseradish Aioli

  • 1/2 cup mayo
  • 1 small clove garlic, grated (even half a clove is plenty)
  • 12 teaspoons horseradish sauce, to taste (I use Boar’s Head)
  • 12 teaspoons lemon juice, to taste
  • salt, to taste


  • Big honking chunk of bread that you really love (I like Trader Joe’s caramelized onion focaccia for this)
  • Pesto rosso (optional as a second sauce)
  • Havarti cheese slices
  • Arugula tossed with olive oil and lemon


  1. Roast the mushrooms: Preheat the oven to 450 degrees. Toss the sliced mushrooms with the avocado oil and the seasoning on a sheet pan until well-combined. Roast for 20-25 minutes, until golden brown.
  2. Make the horseradish aioli: Mix all the sauce ingredients in a bowl until well-combined. Taste and season.
  3. Assemble the sandwiches: Toast the bread for the last few minutes on the pan with the mushrooms. Split the bread, spread with pesto rosso, roasty mushrooms, havarti (pop it in the oven again for a minute if you want it to melt), arugula, and the top piece of bread shmeared with the horseradish sauce. OH MY WORD can you even? This is so good.
  • Prep Time: 10 minutes
  • Cook Time: 30 minutes
  • Category: Sandwich
  • Method: No-cook
  • Cuisine: American

Keywords: mushroom recipe, mushroom sandwich, focaccia sandwich, vegetarian sandwich

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  1. Savory Sojourn Logo

    Happy Monday Lindsay,

    This mushroom sandwich recipe is a game-changer. The depth of flavors – the roasty mushrooms paired with the zesty horseradish aioli can virtually be smelled and felt by others who’ll read this beautiful food blog. Your creativity in the kitchen never ceases to inspire me. Thanks again Lindsay, for sharing another fantastic recipe that’ll keep everyone, including me, coming back for more. Can’t wait to see what you’ll cook-doctor up next. 🙂

  2. Savory Sojourn Logo

    Made these tonight, yum yum yum!
    DO NOT SKIP THE AIOLI (and the pesto Rosso took this sandwich over the top) whole family loved them 🙂

  3. Savory Sojourn Logo

    This is so incredibly good! I made it twice in three days. My husband asked where I got the recipe (which he never does).

  4. Savory Sojourn Logo

    I made this after watching the reel, and it was sooo delicious. The flavors go so perfectly together, and I can’t wait to make it again!

  5. Savory Sojourn Logo

    This sandwich is outstanding. Each component – the two sauces, the roasted mushrooms and the dressed lettuce – come together for a very tasty and satisfying experience. I made this for my husband and he thought I had bought it from a deli … lol! This recipe made it into our rotation. Very grateful.

  6. Savory Sojourn Logo

    LOVED this, however, didn’t have horseradish but had a horseradish sauce (it’s vegan friendly!) and had carmelized onions I added because I didn’t have the TJ focaccia. This sandwich is amazing, secrets in the mushrooms and sauce. SOOOO good!

  7. Savory Sojourn Logo

    Love this recipe!!! Definitely going to be using the horseradish aioli with other meals as well. Thank you!

  8. Savory Sojourn Logo

    After viewing the reel, I recreated this dish, and it turned out incredibly delicious. The flavors complement each other perfectly, and I’m eagerly anticipating making it again!

  9. Savory Sojourn Logo

    Made this dish tonight. It comes together easily and most of the time spent was hands-off, a huge bonus. To add a little protein, I sliced a block of tofu into strips and seasoned with cajun seasoning, then roasted it with the mushrooms. I didn’t use the suggested pesto rosso or fancy foccaccia (just our regular bread), but felt the sandwich worked fine without both. Very enjoyable, and something we will make again.

  10. Savory Sojourn Logo

    Made this tonight and it’s an easy + super delicious and flavorful meal! All of the ingredients shine through and taste incredible melted together!

  11. Savory Sojourn Logo

    This is the best Grilled Mushroom Sandwich with Horseradish Aioli I’ve ever made. I will make this dish for my family following your recipe. I hope it will be delicious

  12. Savory Sojourn Logo

    What an excellent recipe, absolutely delicious. You can’t skip the pesto rosso, the aioli or the arugula. The flavors just pair so perfectly with the mushrooms. Thank you!!

  13. Savory Sojourn Logo

    Are there any specific types of mushrooms that work best for the Roasted Mushroom Sandwich? Are there any specific types of mushrooms that work best for the Roasted Mushroom Sandwich?

    1. Savory Sojourn Logo

      I used closed white mushrooms and had some chestnut mushrooms left over so used both and it was delicious

  14. Savory Sojourn Logo

    This was DELICIOUS! I doubled the mushrooms because I love them. It didn’t take long at all and the payoff of was tenfold. I did use half the recommended amount of seasoning due to the salty factor of my Cajun seasoning and it was still great. Thank you POY!

  15. Savory Sojourn Logo

    Reading all of the other positive comments I really wanted this to be a favourite. It was easy to make but I found the pesto, cajun seasoning, lemon dressing, and aioli to be flavour overload on this sandwich.

    I have tried many recipes from this site with great success and look forward to many more!!

  16. Savory Sojourn Logo

    This was so delicious! “Meaty”, saucy and definitely made a few people jealous at lunch. Lol. My favourite vegetarian lunch so far!

  17. Savory Sojourn Logo

    This was an amazing recipe! My husband and I kept saying “these are so good!” the whole time we ate them. Extra bonus that they were easy to make. Will definitely make these again!

  18. Savory Sojourn Logo

    I didn’t need another reason to love POY, but then you called for a “big honking chunk of bread that you really love” in this sandwich recipe. You speak my language, the language of FOOD! Can’t wait to make this, I have a TJ run coming up and the focaccia is on the list!