In a large bowl combine turkey, egg, breadcrumbs, Pecorino Romano cheese, pepper, garlic powder, onion, mushrooms, parsley, and oregano. Mix well. Gently shape with hands, 1 1/2 inch diameter meatballs and place on greased baking sheet spaced slightly apart. Bake meatballs at 400° F for 20-25 minutes turning once so the meatballs are browned on both sides. Meatballs are cooked at 165°F.