Preheat oven to 400° f.
Add butter to pan, melt, and then add the chopped bell pepper, onion, and mushrooms.
4 tablespoons butter, 1 green bell pepper, ½ yellow onion, 8 ounces package fresh mushrooms
Season with a little salt and pepper if desired and cook, stirring occasionally, until slightly softened.
Cut bread in half and spread bread with mayonnaise and place on rimmed baking sheet.
1 loaf French Bread, 1 tablespoon Mayonnaise -enough to spread over the cut side of the bread
Slice and place cheese on bread.
8 ounces cheese
Add steak, sautéed mushrooms, peppers, and onions. Place more cheese on top of the onions.
Place in oven and cook for 10 to 15 minutes until cheese is melted.
Remove from oven and allow to cool for a few minutes. Slice, serve and watch it disappear!