- Preheat the oven to 400 degrees F.
- Roughly chop the stems and briefly sauté in olive oil.
- Stir together the bread crumbs, stems, Pecorino Romano, garlic, parsley and bell peppers; season with salt and pepper to taste, and blend in 2 tablespoons of the olive oil.
- Drizzle a heavy large baking sheet with about 1 tablespoon olive oil, to coat. Place a tablespoon of the tomato sauce into the mushroom cavities and then spoon the filling into the cavities and arrange on the baking sheet, cavity side up. Drizzle remaining oil over the filling in each mushroom. Bake until the mushrooms are tender and the filling is heated through and golden on top, about 25 minutes. Serve.