Preheat the grill to medium-high. Grill the bread slices until crisp and nicely browned, 2 to 4 minutes per side. Provide each diner with half a tomato and half a garlic clove.
Rub a bread slice with the cut garlic, then with the cut tomato; the idea is to apply a thin film of tomato on the bread. Drizzle each slice with olive oil, sprinkle with salt and pepper and eat at once.