If you love a classic Philly vibe but you are not trying to wrestle with thin-sliced steak on a Tuesday, this vegetarian Philly cheesesteak with grilled portobello mushrooms is your new move. We keep the classic philly cheesesteak ingredients energy (toasty roll, sweet onions, peppers if you want them, and a truly melty cheese situation), but swap in smoky, charred portobellos that taste weirdly meaty in the best way. The little secret here is the quick mushroom marinade plus a simple stovetop cheese sauce that hugs every strip of mushroom like it means it. It eats like a full-on philly cheesesteak sandwich, but it is weeknight-friendly and honestly pretty hard to mess up.
Vegetarian Philly Cheesesteak with Grilled Portobello Mushrooms (So Juicy, So Melty, Zero Beef)
A hearty vegetarian philly cheesesteak recipe with grilled portobello mushrooms, caramelized onions, and a quick provolone cheese sauce on toasted hoagie rolls.
Prep Time 25 minutes mins
Cook Time 25 minutes mins
Total Time 50 minutes mins
Course Main Dish
Cuisine American
large cast-iron skillet or grill pan 12-inch is ideal for good char; use a heavy stainless skillet if that is what you have, or an outdoor grill over medium-high heat
Medium saucepan 2-quart size for the cheese sauce; a small skillet works in a pinch, but a saucepan helps prevent scorching
Tongs makes flipping mushrooms and tossing onions easier; a wide spatula also works
Cutting board and sharp knife portobellos slice best with a sharp chef knife; a serrated knife helps for the rolls
measuring spoons and measuring cup helps keep the sauce consistent; eyeballing is fine once you have made it once
Sheet pan for toasting rolls in the oven; alternatively toast in the skillet cut-side down
For the portobello marinade
- 3 tablespoon olive oil or avocado oil
- 1 tablespoon low-sodium soy sauce or tamari for gluten-free
- 2 teaspoon balsamic vinegar adds that steakhouse-like tang; red wine vinegar also works
- 1 teaspoon smoked paprika optional but highly recommended for grill-y flavor
- 1 teaspoon garlic powder or 2 minced garlic clove
- 1/2 teaspoon black pepper freshly ground if possible
For the veggie filling
- 4 portobello mushroom cap large caps, stems removed; swap with cremini mushrooms if needed, but portobello gives the most "steak" bite
- 2 tablespoon unsalted butter or olive oil for dairy-free (the butter helps with that classic sandwich-shop richness)
- 1 yellow onion thinly sliced; sweet onion is also great
- 1 green bell pepper thinly sliced; optional, but I like the freshness
- 1/2 teaspoon kosher salt plus more to taste
For the quick provolone cheese sauce
- 1 tablespoon unsalted butter helps the sauce stay silky
- 1 tablespoon all-purpose flour use a gluten-free flour blend if needed
- 1 cup whole milk or 2% milk; for dairy-free use an unsweetened oat milk
- 1 1/2 cup provolone cheese shredded or torn into small pieces for faster melting; mild provolone is most classic
- 2 teaspoon nutritional yeast optional but adds a savory "aged" note
- 1/4 teaspoon ground mustard optional, makes the sauce taste more like a real-deal sandwich shop
- 1 pinch cayenne pepper optional, for a gentle heat
For assembling the sandwiches
- 4 hoagie roll or sub roll; choose something sturdy that can handle juicy mushrooms
- 1 tablespoon olive oil for brushing the rolls before toasting (optional)
Prep and marinate
Wipe the portobello mushroom caps clean with a damp paper towel. Scrape out the dark gills with a spoon if you want a cleaner look (totally optional).
In a medium bowl, whisk together 3 tablespoons olive oil, soy sauce, balsamic vinegar, smoked paprika, garlic powder, and black pepper. Slice the portobellos into 1/2-inch strips, then toss them in the marinade until glossy and well-coated. Let them sit while you slice the onion and pepper, about 10 minutes. This short rest is plenty; mushrooms soak up flavor fast.
Grill (or pan-grill) the portobellos
Heat a large cast-iron skillet or grill pan over medium-high heat until it is seriously hot. Add the marinated mushroom strips in a single layer (work in batches if your pan is crowded; crowded mushrooms steam and go soft).
Cook until browned and a little charred on the edges, 4 minutes. Flip and cook 3 minutes more, adding a tiny splash of water only if the pan looks scorched. Transfer mushrooms to a plate. Taste one and adjust with a pinch of salt if needed; soy sauce brands vary.
Cook the onions and peppers
In the same skillet, reduce heat to medium. Add 2 tablespoons butter, then add sliced onion, sliced green bell pepper, and 1/2 teaspoon kosher salt. Cook, stirring and scraping up the browned bits from the mushrooms, until the onions are soft and golden and the peppers are tender, 10 minutes.
Add the grilled mushrooms back to the skillet and toss everything together for 1 minute, just to marry the flavors. Turn off the heat and keep warm.
Make the quick provolone cheese sauce (aka your sandwich glue)
In a medium saucepan over medium heat, melt 1 tablespoon butter. Whisk in 1 tablespoon flour and cook until it smells lightly toasty, 1 minute. Slowly whisk in the milk.
Cook, whisking, until the mixture thickens enough to lightly coat the back of a spoon, 3 minutes. Reduce heat to low and add the provolone a handful at a time, whisking until melted before adding more. Stir in nutritional yeast, ground mustard, and cayenne if using.
If the sauce gets too thick, whisk in 1 tablespoon milk at a time. If it looks grainy, keep the heat low and whisk patiently; high heat is usually the culprit.
Toast and assemble
Heat the oven to 400 F. Split the hoagie rolls and place on a sheet pan cut-side up. Brush lightly with olive oil if you want extra crunch. Toast until the edges are crisp, 5 minutes.
Pile the hot mushroom-onion-pepper mixture into each roll. Spoon the warm provolone sauce over the top (do not be shy; this is the whole point). Serve immediately while everything is hot and melty.
If you want that over-the-top deli feel, you can spoon the filling into the rolls, top with sliced provolone instead of sauce, and briefly broil until bubbly. But the sauce is what makes this philly cheesesteak recipe feel like a proper sandwich-shop situation.
A classic Philly usually means a long roll, thin-sliced beef (often ribeye), and either provolone, American, or Cheez Whiz, plus sauteed onions (peppers are debated). This philly cheesesteak sandwich recipe keeps the roll-onion-cheese formula, but swaps the beef for grilled portobello mushrooms and uses a quick provolone sauce to mimic that melty, drippy finish.
Traditionally it is very thinly sliced ribeye steak (not chicken breast or chicken thigh, and not stew beef). If you want a hybrid version, cook the onions first, then quickly sear thin-sliced ribeye in the same hot pan and proceed with the cheese sauce. The marinade in this recipe is designed for mushrooms, so I would not treat it as a philly cheese steak marinade for steak; beef does better with just salt, pepper, and high heat.
Yes. Use olive oil instead of butter, and replace the provolone sauce with a store-bought dairy-free mozzarella-style shreds melted into unsweetened oat milk thickened with a little cornstarch slurry. Nutritional yeast becomes more important for depth. The overall sandwich will be a little less stretchy, but still very craveable.
Cook the mushroom-onion-pepper filling up to 3 days ahead. Reheat in a hot skillet with a tiny splash of water, stirring just until steaming. The cheese sauce reheats best over low heat with extra milk whisked in. Toast the rolls right before serving so the sandwich stays crisp.
Absolutely. Use a very hot cast-iron skillet and do not overcrowd it. Let the mushrooms sit untouched long enough to brown, then flip. Smoked paprika in the marinade helps mimic outdoor-grill flavor, and the browned bits left in the pan add a ton of depth once you cook the onions.
