Portobello Mushroom Sandwich

Loaded with savory roasted vegetables and melted provolone cheese, this Portobello Mushroom Sandwich is so satisfying even meat-eaters will love it. Perfect for your next Meatless Monday!

Sub roll stuffed with marinated mushroom slices, green pepper, and onions all topped with melty cheese.

If you’ve tried one of our other vegetarian sandwich recipes, like these veggie subs, grilled cheese with apple and havarti, or any of these 25+ vegetarian sandwiches and wraps then you know that we take our sandwich game seriously.

And these cheesy mushroom sandwich melts are no exception. In the last month, Tim and I have made this easy recipe over 5 times and we’re still not sick of it.

Packed with juicy marinated mushrooms, crunchy veggies, and cheese, these meatless subs have the perfect combination of savory flavors in each bite!

Sandwich ingredients arranged on a wood cutting board and labeled.

Ingredient Notes

  • Bell Pepper: I love the slight bitterness of green peppers but you can use a sweeter red, orange, or yellow pepper instead.
  • Portobello Mushrooms: You’ll need one large or two small-ish mushrooms. The gills inside the mushroom are edible and don’t have to be removed. But if they bother you, use a spoon to scrape them out before slicing the mushroom.

Step-By-Step Instructions

Step 1 – Toast The Rolls While You Preheat.

Start by lowering the rack in your toaster oven to the bottom position and preheat to 425°F on the BAKE setting.

Rolls toasting on a cooking rack inside a countertop oven.

One of the best parts of this sandwich is the rolls. They’re crunchy and toasted outside but soft and warm inside.

To achieve this awesomeness, just place your rolls on the rack before you start the oven. If your toaster oven has a traditional temperature dial (and no preheat setting), set a timer for 4 to 5 minutes.

Do I have to use a toaster oven?

Nope! You’ll find directions for cooking this recipe in a traditional big oven, air fryer, or on a stovetop in the recipe card at the end of the post.

Sliced portobello mushrooms marinading in a glass bowl with tongs.

Step 2 – Make the Marinade.

The quick marinade for the vegetables is simple: olive oil, balsamic vinegar, soy sauce, and a few spices. To make it, dump everything in a large bowl and whisk together.

Add the mushrooms to the marinade solo. This gives them a chance to soak up most of it first. Then toss in the pepper and onion slices.

Lastly, rub a rimmed sheet pan with a little oil and pour the veggies onto it.

Marinaded mushrooms, peppers, and onions on a quarter sheet pan.

Step 3 – Roast The Vegetables.

Right about now, the toaster oven should beep that it’s ready. Remove the rolls, set them aside, and add the vegetables.

Stir the pan once or twice while it cooks. Around the 7-minute mark, the mushrooms will begin to release a lot of liquids and your house will start smelling very good.

After about 15 to 18 minutes a little of the liquid will remain but the onions, mushrooms, and peppers will be brown on the edges and have a delicious tender-yet-toothy texture.

Two piles of roasted vegetables with cheese melted on a sheet pan.

Step 4 – Get Metly.

Put on a pair of oven mitts and carefully remove the hot pan. Use a spatula to scooch the roasted vegetables into two piles and top each one with a slice of smoky provolone cheese. To melt the cheese, return the pan to the toaster oven for 2 to 3 minutes.

Step 5 – Assemble Your “Meaty” Meatless Sandwiches.

Split the rolls in half and scoop the filling into each one. For a little spicy kick, sprinkle on a pinch of red pepper flakes. Then grab a few napkins, and enjoy!

Sideview of melted cheese, peppers, and mushroom in a sandwich roll.

How should I store leftovers?

The assembled sandwiches do need to be eaten right away otherwise they will get soggy. If you’re cooking for one, I recommend toasting only a single sub and assembling it.

Store the leftover sub and cooked veggies separately. When ready to eat, warm all of the components in the toaster oven then put them together and enjoy your bonus sandwich.

Closeup of hoagie stuffed with bell peppers, onions and cheese.

More Tasty Vegetarian Sandwich Recipes

Sub roll stuffed with marinated mushroom slices, green pepper, and onions all topped with melty cheese.

Portobello Mushroom Sandwich

Yield: 2 Sandwiches
Prep Time: 15 minutes
Cook Time: 20 minutes
Total Time: 35 minutes

Deeply savory marinated mushroom strips are the star of these sandwiches. Their umami-packed flavors satisfy vegetarians and meat eaters alike!


  • 2 Sandwich Rolls
  • 2 teaspoons (10 grams) Olive Oil, divided
  • 1 tablespoon (15 grams) Balsamic Vinegar
  • 2 teaspoons (15 grams) Low Sodium Soy Sauce
  • 1/2 teaspoon Dried Oregano
  • 1/4 teaspoon Garlic Powder
  • 1/4 teaspoon Black Pepper
  • 1 large Portobello Mushroom (about 4 ounces/114 grams), brushed clean and thinly sliced
  • 1 small Bell Pepper, seeded and thinly sliced
  • 1/2 a small Yellow Onion, thinly sliced
  • 2 slices Provolone Cheese


  1. Adjust the cooking rack to the bottom position, select the BAKE setting, and preheat the toaster oven to 425°F. While the oven preheats, place the sandwich rolls inside to warm and toast.
  2. Rub a rimmed sheet pan with 1 teaspoon of the oil.
  3. In a large bowl, whisk together the remaining 1 teaspoon of olive oil, balsamic vinegar, soy sauce, oregano, garlic powder, and pepper. Add the mushrooms and stir to coat well with the sauce. Stir in bell pepper and onion. Pour vegetables onto the prepared pan.
  4. Once the oven has preheated, remove the sandwich rolls and add the vegetables.
  5. Roast vegetables, stirring occasionally, until fork-tender, about 15 to 18 minutes minutes.
  6. Carefully remove the pan and divide the veggies into two piles on the pan. Top each pile with a slice of provolone cheese. Return the pan to the toaster oven and cook until the cheese is melted about 2 to 3 minutes.
  7. Split the rolls in half, scoop the filling into each one, and dig in!


Mushrooms: The gills inside the mushrooms are edible and do not need to be removed. If they bother you, use a spoon to scrape them out before slicing the mushroom.

Bell Peppers: A Green, Red, Orange, or Yellow bell pepper can be used. The colored peppers will taste sweeter in the sandwich.

Rolls: If you don't have rolls, the peppers and cheese also taste delicious sandwiched between slices of toasted bread.

Alternative Cooking Methods

Full-Sized Oven: Skip toasting the rolls during the preheating. Follow the remaining directions, adding the rolls to the oven during the last 5 to 7 minutes of the cooking time.

Stovetop: Heat 1 teaspoon oil in a large skillet over medium heat. Add marinated vegetables and saute for 7 to 9 minutes until softened and browned. Top with cheese and heat until melted, about 2 minutes. Warm buns in the toaster oven or split and toast using another skillet.

Air Fryer: Heat the air fryer to 400°F, use tongs to transfer marinated vegetables to the air fryer basket. Air fry until the veggies are browned and tender, about 12 minutes, tossing the basket halfway through cooking. Split the rolls, top them with the veggies and cheese, then carefully add the subs to the air fryer basket. Heat at 350°F until the cheese is melted about 4 or 5 minutes.

Nutrition Information:
Yield: 2 Serving Size: 1 Sandwich
Amount Per Serving: Calories: 407Total Fat: 15.5gSaturated Fat: 5.5gCholesterol: 19mgSodium: 720mgCarbohydrates: 51.5gFiber: 6gSugar: 7.1gProtein: 16.4g

Leave a Reply

Your email address will not be published. Required fields are marked *