Toast or grill sliced baguette until golden and crisp
Rub hot bread with cut side of garlic clove
Drizzle generously with olive oil and sprinkle with salt
Cut tomatoes in half, scoop out seeds, salt lightly, and drain cut-side down for 15 minutes
Dice drained tomatoes finely and mix with onion, minced garlic, olive oil, balsamic vinegar, salt, pepper, and optional basil
Cover mixture and marinate at least 4 hours or overnight
Spoon tomato topping onto bread just before serving
Optionally add mozzarella, drizzle more balsamic, and garnish with basil