1. Prepare grill.
2. Combine the first 5 ingredients in a medium bowl; stir in 1/4 teaspoon salt and 1/4 teaspoon freshly ground black pepper. Toss gently to coat.
3. Brush fish with oil; sprinkle evenly with remaining 1/4 teaspoon salt and 1/4 teaspoon black pepper. Place fish on grill rack coated with cooking spray; grill 2 minutes on each side or until fish flakes easily when tested with a fork or until desired degree of doneness. Serve with tomato mixture; garnish with dill sprigs, if desired.