Preheat a grill pan or outdoor grill to medium-high heat (about 400°F / 200°C). Brush both sides of the sourdough slices lightly with 2 tablespoons of the extra-virgin olive oil. Place bread on the hot grill or grill pan and cook 1.5–2 minutes per side, until charred grill marks appear and the bread is crisp but still slightly tender inside. Remove and arrange on a work surface.

While the bread is still warm, rub the top of each slice once with the cut side of the garlic clove to impart a gentle garlic aroma. Reserve the remaining 1 tablespoon olive oil for the tomato topping if desired.

Lightly season the grilled slices with a pinch of salt and a grind of black pepper to taste (use from the salt and pepper listed in this section).

Tomato topping

Prepare tomato mixture

Core and finely dice the tomatoes, discarding seeds if very watery. Place diced tomatoes in a medium bowl. Finely mince the shallot and add to the tomatoes. Add the sliced basil (reserve a few whole small leaves for garnish) and stir gently.

Add 1 tablespoon olive oil (from the second olive oil amount), the lemon juice, 1 teaspoon salt, and 1/2 teaspoon black pepper to the tomato mixture. Stir to combine and taste; adjust seasoning. Let the mixture sit 5–10 minutes so flavors meld and excess liquid drains slightly.

Assemble & finish

Top bread and cheese

Spoon about 2–3 tablespoons of the tomato mixture onto each grilled sourdough slice, allowing any excess liquid to stay in the bowl so the bread doesn't get soggy. Top each with roughly 1 ounce (about a golf-ball amount) of torn or sliced fresh mozzarella, pressing gently so it nestles into the tomatoes.

If desired, place the assembled slices briefly (30–60 seconds) under a broiler or on the warm grill just to warm the cheese slightly—do not melt it completely; the cheese should stay soft and slightly creamy.

Finish and serve

Drizzle each bruschetta lightly with 2 tablespoons total of balsamic glaze over the batch (about 1/4–1/2 teaspoon per slice), scatter reserved basil leaves on top, and finish with a light sprinkle of flaky sea salt if using. Serve immediately while the bread is still warm and crisp.