1Heat coals or gas grill for direct heat. If fish fillets are large, cut into 6 serving pieces. Place fish in heavy-duty aluminum foil bag. Mix olives, capers, tomato, onions and garlic; spoon over fish. Drizzle with lemon juice. Sprinkle with salt and pepper. Double-fold open end of bag.
2Cover and grill bag 5 to 6 inches from medium heat about 15 minutes or until fish flakes easily with fork. Place bag on serving plate. Cut large X across top of packet; fold back foil. Serve fish with lemon wedges.