Cut the ciabatta into thin slices. Cut bread slices in half. Heat 4-6 tablespoons of oil in portions in a large frying pan. Fry the bread in it in portions on each side until golden brown and take it out. Season with salt.
Peel onions and cut them into thin slices. Wash the tomatoes and cut them into quarters or eighths. Wash basil, shake dry, pluck off leaves. Cut mozzarella into thin slices.
Mix wine vinegar, salt, pepper and approx. 1 teaspoon sugar well. Fold in 6 tablespoons of oil. Mix roasted ciabatta, onions, tomatoes, basil, mozzarella and vinaigrette. Leave to stand for about 1 hour.
Season salad again with salt and coarse pepper.