Slice the green peppers in half and clean. Set aside. Slice your banana pepper in strips.
Slice onions and mushrooms. In a frying pan saute' in butter with garlic the mushrooms and onions. While the mushrooms, onions, and garlic are cooking, rough chop the roast beef.
Add the roast beef to the mixture in the frying pan and cook for about 5 minutes till all melds together.
To build your peppers lay a slice of cheese into the green peppers. Fill the pepper with the meat mixture clear to the top of the pepper. Lay slices of the banana peppers over the meat mixture and top with another slice of provolone.
Bake for 30 minutes until peppers are tender and cheese is brown.
Take the chopped lettuce and tomatoes and mix with mayonaise and top the peppers before serving.