Slice peppers in half lengthwise, remove ribs and seeds.Slice onions and mushrooms. Saute over medium heat with butter, olive oil, minced garlic and a little salt and pepper and italian seasoning, Saute until onions and mushroom are nice and caramelized. About 25-30 minutes.Preheat oven to 400 .Slice angus roast beef into thin strips and add to the onion/mushroom mixture. Allow to cook 5-10 minutes.Line the inside of each pepper with a slice of provolone cheese.Fill each pepper with meat mixture until they are nearly overflowing.Top each pepper with another slice of provolone cheese.Bake for 15-20 minutes until the cheese on top is golden brown.