Place the diced tomatoes in a bowl and gently toss with 2 tablespoons olive oil, a pinch of flaky salt, and a few grinds of black pepper.
If your tomatoes are especially juicy (as heirlooms often are), let the diced tomatoes sit in a colander for 5–10 minutes before tossing them with the olive oil. They'll still be juicy, but they won't make the bread soggy while baking.
Arrange the baguette slices on a baking sheet and lightly drizzle each slice with the remaining 1 tablespoon olive oil.
Slice the garlic clove in half and rub it on each slice of bread. This helps infuse a light garlic flavor without being overpowering.
Spoon the tomato mixture onto each slice of bread.
Bake for 12–15 minutes, or until the bread is lightly crisp around the edges and the tomatoes have softened just slightly.
Remove from the oven and immediately top with fresh basil.
Finish with a light drizzle of olive oil, a drizzle of balsamic glaze (or balsamic vinegar), and a sprinkle of flaky sea salt.
Serve warm or at room temperature
The secret is using tomatoes that are truly in season. Mixing several varieties of heirloom tomatoes creates layers of sweetness, acidity, and texture that make this simple appetizer taste like something you'd enjoy at a café in Italy.