Trim and pull the mushrooms: cut off the tough end of each oyster mushroom stem. Tear the caps and stems by hand into thin, shredded pieces.

Make the marinade: in a bowl whisk together 4 Tbsp olive oil, 1 tsp vegan Worcestershire sauce, 1 tsp soy sauce or tamari, 1/4 tsp balsamic vinegar, 1 tsp oregano, 1/2 tsp ground cumin, 1/2 tsp sweet smoked paprika, 1 tsp garlic powder, 1 tsp onion powder, 1/2 tsp salt, and 1/8 tsp black pepper.

Marinate the mushrooms: add the shredded mushrooms to the bowl and toss to coat evenly. Let sit 5–10 minutes. If any marinade remains in the bowl, set it aside (you can add a little back to the pan later if needed).

Prepare the onion: peel and thinly slice the medium onion.

Caramelize the onion: heat a non-stick skillet over medium heat and add 1 Tbsp olive oil. Add the sliced onion and cook, stirring occasionally, until golden brown and soft, about 5–8 minutes. Transfer the cooked onion to a plate and set aside.

Cook the mushrooms: wipe the skillet if it has burnt bits, then heat it over medium-high to high. Add the marinated mushrooms in a single layer (work in batches if necessary to avoid crowding). Stir occasionally and cook until the mushrooms are well browned and crispy at the edges, about 10–15 minutes. If the pan seems dry and you reserved some marinade, add a teaspoon of the reserved marinade to the pan.

Combine mushrooms and onions: return the cooked onions to the skillet with the mushrooms and toss briefly to combine and reheat, about 1 minute.

Add the cheese and melt: place the 3–4 oz vegan provolone evenly over the mushroom-and-onion mixture. Cover the skillet with a lid until the cheese melts, about 1–3 minutes.

Serve immediately: transfer the melted mushroom-and-cheese filling to plates or use as desired for sandwiches/rolls and enjoy.