Turn the broiler on in the oven.
Add the sliced onion, bell pepper and mushrooms to large skillet and saute until tender. Season with salt and pepper. Remove from the skillet and set aside on a plate.
Add the olive oil to the same skillet and saute the thinly sliced meat in the veggie juices. Saute for a few minutes, or until cooked through. Add the veggies back in with the sauteed beef. For the cheese, you can melt it into the meat-veggie mixture, or you can add it on top of the meat once you assemble the sandwiches.
Add of the meat-veggie mixture to each of the hoagie or sub rolls. Add 2 slices of cheese on topand place them all on metal baking sheet.
Run them under the broiler for 2 to 3 minutes, or until cheese is melted and bread begins to golden.
Serve Philly Cheesesteak Sandwiches with fruit and chips.