Preheat the broiler.
Heat the EVOO, 2 turns of the pan, in a deep skillet or a heavy-bottomed pot over medium-high heat. Add the mushrooms and brown 5 minutes. Add the beef and cook, breaking it up with a wooden spoon, until browned, 7-8 minutes. Add the bell pepper, onion, garlic, oregano or marjoram, and red pepper flakes; season with salt and pepper and cook 5 minutes. Stir in the tomato paste, then add the wine and cook another minute. Add the beef stock, Worcestershire sauce and crushed tomatoes or tomato sauce. Stir in the parsley and simmer a few minutes to thicken.
While the filling is simmering, toast the rolls: Brush the cut sides with butter, top with some cheese, and broil to brown.