1Heat gas or charcoal grill. Drizzle both sides of tuna steaks with oil; rub with garlic. Let stand at room temperature 15 minutes to marinate.
2Meanwhile, on large serving plate or platter, place tomato and cheese slices. Drizzle with vinaigrette; sprinkle with basil. Set aside.
3Place tuna on grill. Cover grill; cook over medium heat 8 to 10 minutes, turning once, until fish flakes easily with fork and is slightly pink in center. Cut tuna into slices. Place tuna slices on top of tomatoes and cheese.