Combine vinegar, salt, pepper, and olive oil. Stir in tomatoes and basil. Set aside
Toast bread on hot grill (or toaster or broiler) until both sides are golden brown. Brush one side of each slice with garlic oil and set aside, uncovered, to cool to room temperature.
Tear the bread into pieces ~3/4” square.
Toss bread, cucumbers, and onion with the tomato mixture. Cover with plastic wrap and marinate at room temperature for at least 20 minutes, or as long as 4 hours. Bread will soften as it absorbs flavors in the salad.