Prep all ingredients by dicing the onion and green bell pepper, and slicing the mushrooms.
Heat olive oil in a large skillet over medium heat. Sauté diced onion and green bell pepper for 5 minutes until soft. Add ground beef and cook for 7-10 minutes until browned. Season with garlic powder, onion powder, salt, and pepper.
Add sliced mushrooms to the skillet and cook for an additional 3-4 minutes. Pour in heavy cream, Worcestershire sauce, and Italian seasoning. Stir until well combined. Remove from heat and fold in half of the provolone and mozzarella cheeses.
Transfer the mixture to a greased 9x13-inch baking dish. Spread evenly and sprinkle remaining provolone, mozzarella, and Parmesan cheese on top.
Preheat oven to 350°F. Bake casserole for 25-30 minutes until cheese is melted and bubbly. Let cool for 5-10 minutes before serving.