Preheat oven to 350°F (177°C). Line a baking sheet with aluminum foil. Place baguette slices on the baking sheet and brush with olive oil. Bake for 10 minutes and remove from oven, leaving oven on.
Meanwhile, dice tomatoes and mince garlic. In a medium bowl, stir together remaining olive oil with tomatoes, garlic, balsamic vinegar and salt.
Place a slice of mozzarella on each bread slice, then top with tomato mixture. Bake for an additional 6 minutes. Remove from oven. Drizzle lightly with olive oil, top with chopped basil leaves and freshly-cracked pepper. Serve hot.