Preheat oven to 425°.
Place fish in an 11″ x 7″ baking dish coated with cooking spray. Combine lime juice, mayonnaise, onion powder, and pepper in a small bowl, and spread over fish. Sprinkle with breadcrumbs; drizzle with butter. Bake at 425° for 20 minutes or until fish flakes easily when tested with a fork. Sprinkle with parsley optional.