Scrape the stones out of the melon, cut off the skin, dice the pulp in the bowl and put it in the fridge.
Mix the lemon juice, oil, balsamic vinegar, salt, pepper and sugar well in a bowl. Dice in the mozzarella, season again with pepper, stir and let steep in the refrigerator for 15 minutes.
Then pour the mozzarella with the vinaigrette over the cucumber and melon pieces, mix well and season to taste. Cut the basil leaves into fine strips and fold into the salad.
Fill the salad into portion bowls, garnish and serve.