Brush grill rack with vegetable oil. Heat coals or gas grill for direct heat. In shallow glass or plastic dish or resealable food-storage plastic bag, mix lemon juice, 1 tablespoon oil, the salt, pepper and garlic. Add fish; turn several times to coat with marinade. Cover dish or seal bag and refrigerate 10 minutes.
Remove fish from marinade; reserve marinade. Cover and grill fish 4 to 6 inches from medium heat 10 to 15 minutes, turning once and brushing with marinade, until fish flakes easily with fork. Discard any remaining marinade.