Portobello Mushroom Sandwich (Grilled or Pan Seared!)

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Craft an epic Portobello Mushroom Sandwich, loaded with balsamic marinated portabella mushrooms, Swiss cheese, roasted red peppers, microgreens, and a secret special sauce! This super satisfying mushroom burger is perfect for a quick weeknight dinner or cookout!

The Anatomy of an Epic Portobello Sandwich

Portobello mushroom sandwich featured on a black plate with a wedge of Swiss cheese in the background.

If we ever opened a NeighborFood restaurant, our specialty would be sandwiches. Sandwiches are quick to make, but deliver BIG in flavor. They can be hot or cold, meaty or vegetarian, healthy or a worthwhile splurge. This Vegetarian Mushroom Sandwich falls in the warm and healthy (but oh-so- satisfying) camp.

Over the years, we’ve experimented with dozens of different sandwich recipes, and we’ve learned a few things along the way. From a stack of gloriously gooey Apple Brie Grilled Cheese to the deceptively simple classic Scrambled Egg Sandwich, there are four elements that take any sandwich from good to great.

Good bread– This is not a place to skimp. We’re talking chewy ciabatta, herby focaccia, a puffy sweet Brioche. A great sandwich starts with great bread.
Special sauce– Plain mayo is fine, but all the best sandwiches have a special sauce. Whether it’s homemade pesto or Big Mac sauce or the chipotle mayo we use on our Turkey Avocado Sandwich, a secret sauce adds creaminess and prevents the sandwich from being dry.
Layers of filling– Whether you’re making a vegetarian mushroom sandwich or a meaty Skirt Steak Sandwich, you’ll want to layer different flavors and textures together. Add crisp lettuce or microgreens or pile on juicy tomato and crunchy radish. The options are endless!
Cheese– Sliced cheese, shredded cheese, or cream cheese, this is an essential ingredient in all of our sandwich recipes.

Today, we’ll use the four building blocks of a great sandwich to make the ultimate Grilled Portobello Mushroom Sandwich. This sandwich delivers big, bold flavors in a package that will be loved by meat eaters and vegetarians alike.

Key Ingredients

Portobello mushrooms in a glass casserole dish surrounded by ingredients for a sandwich.

Bread– A soft, puffy Brioche roll is the perfect size and shape for a portobello mushroom burger.
Mayo + Lemon + Garlic + Herbs– A bright garlic aioli is the secret sauce that makes this sandwich pop.
Portabella Mushrooms– Portabello mushrooms are a large variety of mushrooms with a rich, umami flavor. Their bigger size makes them perfect for stuffing, grilling, and in plant based burgers. They can also be chopped up and used in recipes like Parmesan Leek and Mushroom Pasta or Creamy Mushroom Soup.
Balsamic Vinegar + Garlic + Soy Sauce + Lemon Juice– A flavor packed savory marinade for the mushrooms with a hint of sweetness and citrus.
Swiss Cheese– Melty, gooey Swiss cheese pairs beautifully with mushrooms and makes this sandwich extra satisfying. Swiss and other cheeses like mozzarella and cheddar are also a great source of protein for a plant based sandwich. I used Guggisberg Baby Swiss for this recipe, but you could also substitute gruyere on another cheese of your choice.
Greens– We use both lettuce and microgreens to add some fresh green goodness to the sandwiches.

For a full list of ingredient amounts, visit the recipe card below.

How to Buy, Store, and Clean Portobello Mushrooms

When shopping for portobellos (or any mushroom, really), look for caps that are firm and dry, without any slimy or mottled spots. Store the mushrooms in the container you bought them in until you’re ready to cook them.

Use a slightly damp paper towel to wipe away any dirt from the surface of the mushrooms before cooking. You’ll also want to remove the thick, woody stem. I find the easiest way to remove the stem is to place a finger on either side of the stem, then use your other hand to gently work the stem back and forth until it pops out.

Four grilled portobello mushrooms with melted cheese on top.

How to Grill Portobella Mushroom Sandwich

Balsamic marinade being poured onto a portobello mushroom.

Step 1: Marinate the mushrooms. Whisk together olive oil, garlic, balsamic vinegar, lemon juice, soy sauce, and salt and pepper. Pour over the mushrooms. Cover and refrigerate at least 30 minutes or up to 12 hours.

Step 2: Prep the grill. Clean and oil the grill grates, either by rubbing with an oil soaked paper towel or spraying with cooking spray. Preheat to medium heat (375-400 degrees).

White casserole dish filled with four portobello mushroom caps in a balsamic marinade.

Step 3: Grill. Place the mushrooms directly on the grill grates cap side down, and grill undisturbed for 3-4 minutes per side, or until the mushrooms are softened and take on a rich, brown color. Add cheese slices for the last minute.

Open face portobello sandwich topped with roasted red pepper slices and microgreens.

Step 4: Assemble. Spread the aioli on both sides of the buns. Top with lettuce, then mushrooms, roasted red peppers, and microgreens. Serve.

Storage and Make Ahead Instructions

The marinade and the aioli can be made up to 3 days in advance and stored in the fridge.
Mushrooms can be marinated up to 12 hours.
Leftover mushrooms keep well in an airtight container in the fridge for up 4 days.
Reheat mushrooms on the stove top or in the microwave.

Sandwich stacked with a marinated portobello mushroom, red pepper slices, and microgreens.

Variations + Tips

Make them vegan! For a vegan mushroom sandwich, swap the mayo for eggless mayo, and omit the cheese or use vegan cheese.
Experiment with toppings– These would also be lovely with sun dried tomatoes, avocado, red onions, spinach, or arugula. Goat cheese would be absolutely fabulous, or you could add a little funk with blue cheese.
Pair dairy foods with plants to create a nutritional powerhouse, including vital nutrients like calcium, vitamin D, potassium, and fiber. I use this combo in the Best Ever Veggie Sandwiches as well as in this Veggie Pizza, Caprese Panini, and Roasted Broccoli Cheese Casserole.
Use leftover aioli on Grilled Burgers or in Roasted Red Pepper Turkey Wraps.
Love the combination of mushroom and Swiss, but miss the meat? Try these Mushroom Swiss Burgers!

FAQs

How long do you marinate mushrooms?

Mushrooms soak up a marinade quite quickly. I prefer to marinate mushrooms for at least 30 minutes for the best flavor, but they can go as long as 12 hours. Toss together the marinade in the morning, and it’ll be ready for you at dinner time! Be sure the marinade covers both sides of the mushroom. I prefer to marinate them gill side up, so the marinade can soak into it.

Can I grill portobella mushrooms in a pan?

Yes! Heat a grill pan over medium high heat. Add the mushrooms, cooking each side for 3-4 minutes, or until well seared.

Portobello mushroom sandwich on a brioche roll.

More Vegetarian Sandwich Recipes to Enjoy

Who says you need meat to make a great sandwich? Try these amazing plant based and vegetarian sandwiches next time you need a sandwich fix!