Prepare grill for cooking at medium high heat. Slice onion, bell pepper and zucchini and set aside. Press garlic into small bowl and add tomatoes.
Cut four 18 x 12 inch pieces of heavy duty aluminum foil. Place one fourth of the onion, bell pepper and zucchini slices in center of each piece of foil. Spoon ¼ cup tomato mixture over vegetables; top with 1 fish fillet. Spray fish fillets with olive oil cooking spray. Sprinkle with salt and fresh ground black pepper.
Top each fish fillet with remaining tomato mixture and 3 sliced olives. Fold foil over fish and vegetables and double fold edges to seal, leaving room for steam inside of each foil packet.
Place foil packets on grill grid and grill for 18 to 20 minutes or until fish flakes easily with fork. Remove foil packets from grill. Open with care and allow steam to escape.
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