In a bowl, combine the tomatoes, mango, onion, cilantro, lime juice, vinegar and sugar. Stir in 1/2 teaspoon salt, 1/2 teaspoon pepper, and garlic.
Brush halibut with oil; season with 1/2 teaspoon salt and 1/2 teaspoon pepper. Place fish on grill rack; grill 3 minutes on each side or until fish flakes easily when tested with a fork. Serve with mango salsa.