Preheat broiler to high. (If you prefer, you may also grill the bread)
Combine the oil and mashed garlic in a small bowl.
Brush oil mixture onto each slice of bread and place bread slices on a baking sheet.
Toast bread on each side under the broiler...keep an eye on it so it doesn’t burn.
Chop seeded tomatoes and capers and place in a small bowl.
Add the onion and mozzarella.
Pile basil leaves on top of one another and roll into a log.
Thinly slice basil into green confetti and loosely combine with tomatoes.
Add remaining oil and garlic mixture, balsamic vinegar and a little coarse salt and cracked black pepper to the bowl and gently toss to coat.
Cover and refrigerate until ready to use.
Right before ready to serve, top toasted bread with mixture and place o baking sheet.
Broil until cheese is just melted. Serve hot.