2 cups assorted cherry tomatoes, halved (or quartered if large)
1/2 small red onion, finely chopped
3 Tbsp Extra-Virgin Olive Oil, plus additional for brushing
1 Tbsp basil
1 1/2 Tbsp Traditional Balsamic Vinegar
1 large loaf focaccia, halved horizontally (reserve half for another use)
1 garlic clove, peeled, halved
Combine halved tomatoes, finely chopped onion, 3 tablespoons olive oil, basil, and balsamic vinegar in medium bowl; season tomato topping with salt and pepper.
DO AHEAD: Topping can be made 2 hours ahead. Cover and let stand at room temperature, tossing occasionally.
Preheat broiler or grill.
Brush bread with olive oil. Place focaccia cut side up on baking sheet if using broiler; cut side down if using grill.
Toast bread until top is golden brown, watching closely to avoid burning, about 2 minutes. Immediately rub cut side of bread all over with halved garlic, then cut focaccia crosswise into 4 equal pieces.
Top toasted focaccia with tomato mixture and serve.