Preheat oven to 325º. Place peppers in a large baking dish and bake until tender, 30 minutes.
Meanwhile, in a large skillet over medium-high heat, heat oil. Add onions and mushrooms and season with salt and pepper. Cook until soft, 6 minutes. Add steak and season with more salt and pepper. Cook, stirring occasionally, 3 minutes. Stir in Italian seasoning.
Add provolone to bottom of baked peppers and top with steak mixture. Top with another piece of provolone and broil until golden, 3 minutes.