Preheat oven to 400 ̊ F.
Prepare Gary's QuickSteak Sirloin Beef according to package directions Add package of Wow! Seasoning and Worcestershire Sauce. Stir to combine.
Slide meat to one side of skillet. Add butter and begin to melt, then add diced peppers, onions, and mushrooms. Sauté two to three minutes, set aside.
Place bread on cookie sheet.
Mix mayonnaise with mustard, spread on both halves of bread.
Place 6 to 8 slices of the provolone cheese on top of mayonnaise mixture, top with beef and vegetables, layer with remaining cheese slices.
Cook 10 to 15 minutes on middle oven rack until browned and cheese is bubbly
Cut into three-inch slices, serve immediately