1) Preheat the oven to 200°C.
2) Stir the breadcrumbs, Pecorino Romano, garlic, parsley, mint, salt and pepper, to taste, and two tablespoons olive oil in a medium bowl to blend.
3) Drizzle a heavy large baking sheet with about one tablespoon olive oil, to coat. Spoon the filling into the mushroom 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.