Roasted Mushroom Sandwich with Horseradish Aioli Recipe - Pinch of Yum
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Roasted Mushroom Sandwich with Horseradish Aioli

2 reviews / 5 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. Pinch of Yum 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. Pinch of Yum Logo
    Margaret Hill

    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. Pinch of Yum 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).