1In medium bowl, gently toss tomato, cheese, olives and 1 tablespoon of the basil. Cover and refrigerate until serving.
2Spray grill rack with cooking spray. Heat coals or gas grill for direct heat.
3In small bowl, mix remaining 2 tablespoons basil, the oil, garlic salt and pepper. Brush mixture over tuna.
4Grill tuna uncovered 4 inches from medium-high heat 5 minutes. Turn carefully; brush with any remaining oil mixture. Grill 10 to 15 minutes longer or until tuna flakes easily with a fork. Serve topped with tomato mixture.