Wash the potatoes. Cook in boiling water for 15-20 minutes. In the meantime, cover 2 slices of mortadella with 1 slice of cheese each. Place the rest of the mortadella on top, roll up tightly and chill. Wash the cucumber, cut half into thin slices and grate the rest coarsely.
Clean, wash and dice the peppers. Mix quark, milk, grated cucumber and half of the paprika cubes. Season with salt and pepper. Clean, wash and pluck lettuce and rocket into small pieces. Peel and slice the potatoes cold. Mix vinegar, salt, pepper and sugar. Whip the oil into it. Mix potatoes and marinade. Cover and leave to stand for about 30 minutes. Season to taste again.
Whip the oil into it. Mix potatoes and marinade. Cover and leave to stand for about 30 minutes. Season to taste again. Arrange potatoes and cucumber on the salads. Cut the mortadella rolls into slices. Serve sprinkled with some tzatziki, remaining paprika cubes and roasted mustard seeds