Preheat oven to 375 °F (191 °C). Place the two sliced sub rolls on a two pieces of aluminum foil. Set aside.
2 hoagie rolls
In a large skillet, saute onions and green peppers for about 3-4 minutes.
1 medium onion, 1 medium green pepper
Add in the mushrooms, and cook until softened, about 3 minutes. Place in a bowl and set aside.
6 ounce portobello mushrooms
In the same skillet, cook the steak until all is cooked through, about 5 minutes.
3/4 pound thinly sliced ribeye steak
Add the onions and peppers back into the skillet and toss together (seasoning with salt and pepper, to taste).
Salt and pepper
To assemble the cheesesteaks: open one sub roll and add in half of the meat filling then top with half the provolone cheese. Repeat for the second sub roll.
1 cup shredded provolone cheese
Tightly wrap each sub in aluminum foil then place directly on the oven rack for 15 minutes.
After 15 minutes, remove from oven and your cheesesteak sandwich is ready for you to unwrap (carefully) and enjoy!