Heat gas or charcoal grill. Cut 1 (24x18-inch) sheet of heavy-duty foil; spray with cooking spray. Layer coarsely chopped onion, bell pepper and tomatoes on center of sheet. Bring up 2 sides of foil over vegetables so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Fold other sides to seal.
Place vegetable packet on grill over medium heat. Cover grill; cook 6 minutes, turning once. Meanwhile, in large bowl, mix onions, vinegar, salt, thyme and pepper sauce; set aside. Cook rice in water as directed on package.
Spray fish and grill basket that has locking top with cooking spray. Place fish in basket. Place on grill with vegetable packet. Rotate vegetable packet 1/2 turn. Cover grill; cook 8 to 12 minutes, turning fish once, until fish flakes easily with fork.
Place fish on serving platter; keep warm. Cut large X across top of packet; carefully fold back foil to allow steam to escape. Add grilled vegetables and parsley to green onion mixture; toss. Spoon over fish. Serve with rice.