Caramelize onions over medium low heat, stirring occasionally till caramelized and nicely browned about 7mins. Add in peppers and mushrooms. Stir to cook slightly (you want it tender but not fully cooked)
Add in beef, salt, pepper and garlic powder. Stir around. In a bowl mix melted butter, heavy cream & Parmesean cheese. Throw that mixture into the beef.
In a casserole dish, brush lightly with olive oil. Place a layer of cutdacarb bread, brush with some mayo and add in the beef mixture – top with three slices of provolone. Repeat with two more layers.
add one last cutdacarb layer, brush lightly with oil, and top with Mozzarella; sprinkle some black pepper
Bake at 400°F for 15-20mins. Broil the top until cheese is bubbly (about 3-4mins).