Set the oven to 350°F before baking.
Cut the rolls into halves, and then place the bottom halves in a 11" x 7" baking dish or on a baking sheet.
Add the desired amount of salt and pepper to the steak, then cook it on a skillet. Once it's done, remove it from the skillet and let it rest.
Sauté the onions and peppers until they are soft.
Apply a thin coating of mayonnaise on both sides of the rolls.
Divide the cooked steak, onions, and peppers evenly among the bottom halves of the rolls in the baking dish.
Cover the peppers and onions with a layer of provolone cheese.
Combine melted butter and 1 tablespoon of diced raw onions in a small bowl.
Place the top halves of the rolls on the cheese, then spread the butter mixture over them.
Place foil over the sandwich casserole and bake for 10 minutes. Take off the foil and bake for an extra 10 minutes, or until the cheese is melted.
Slice and serve the sandwich casserole.