Wash fish & pat dry. Sprinkle with salt & pepper & dot with butter. Arrange overlapping slices of onion, lemon & parsley in cavity of fish; brush fish with oil. Wrap in heavy duty aluminum foil, sealing edges with double folds. Place on grill over med hot coals; cook, carefully turning salmon every 10 minutes. Test for doneness after 45 minutes by inserting meat thermometer into thickest portion. Cook to internal temperature of 160. To serve, transfer fish to heated platter; fold back foil. Cut between bone & meat with wide spatula; lift off each serving. Serve with Zesty Sauce.