Wash and quarter the tomatoes, remove the stem and the seeds. Dice approx. 0.5 cm in size. Peel onion and garlic and chop finely. Finely pluck the basil, set aside a few leaves for the garnish.
Heat the olive oil in a pan. Sweat the onion and garlic for approx. 5 minutes. Add the tomatoes and basil, stir, season with salt and pepper and allow to cool in a large bowl.
Melt some butter for the gnocchi in a large pan. Fry the gnocchi for approx. 5 minutes until golden brown and add to the tomato mixture. Allow to cool slightly.
Drain the mozzarella, cut in half and cut the halves into approx. 0.5 cm wide slices. Put in the salad. Let it steep for about 10 minutes. Garnish with basil leaves and, if desired, serve drizzled with olive oil.