1Heat gas or charcoal grill. In medium nonmetal bowl, mix tomatoes, olives and pesto.
2Place fish on 24x12-inch sheet of heavy-duty foil. Sprinkle salt and pepper over fish. Top with tomato mixture. Bring up 2 sides of foil over fish so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space on sides for heat circulation and expansion. Fold other sides to seal.
3Place on grill over medium heat. Cover grill; cook 20 to 30 minutes or until fish flakes easily with fork. Top with parsley.