To prevent fish from breaking up, it is best to cook them in a greased wire basket made for grilling fish. Sprinkle the inside cavity of the fish with garlic powder. Rub or brush the cavity and skin with vegetable oil. Place in the greased wire basket and grill about 6 inches from coals for 7 minutes on each side. If not using a basket, cover head and tail of fish with foil. (This prevents drying out and makes them easier to turn.) Place directly on the greased grill. Use a greased spatula for turning.
Prepare the lemon-onion butter by stirring the butter with 1 tbsp. lemon juice, peel, onion and seasonings. Serve along with the grilled fish.