Slice the ciabatta into approximately 1.5 cm thick slices and brush them with olive oil. Place on a baking sheet and toast in the preheated oven (180 °C fan) for about 5 minutes until crispy.
Meanwhile, peel and halve the garlic. Once the bread is warm, rub the cut side of the garlic clove over the toasted bread slices.
Wash the tomatoes, halve them, and remove the stem and seeds. Cut the flesh into small cubes. Peel and finely dice the onion. Wash the basil, shake dry, pluck the leaves from the stems, set some aside, and slice the rest into thin strips. Mix tomatoes, onions, and basil in a bowl. Add 3 teaspoons of olive oil, gently combine, and season with salt, pepper, and a pinch of sugar.
Evenly distribute the tomato mixture over the bread slices. Garnish with the remaining basil and serve immediately.