Clams Casino with Pancetta Cooking spray $ 3/4 cup finely diced pancetta 2 tablespoons dry white wine 1/3 cup finely diced red bell pepper $ 3 tablespoons minced shallots 1 garlic clove, minced 1 (1 1/2-ounce) slice day-old country white bread $ 1 1/2 tablespoons grated fresh Parmigiano-Reggiano cheese 2 teaspoons finely chopped fresh parsley 1/4 teaspoon black pepper 36 littleneck clams, cleaned $ Lemon wedges (optional)