Peel and finely chop the onion. Add the tomatoes and 5 tablespoons of water to a pot. Bring to the boil, stir in the stock and season with salt, pepper and sugar. Simmer at low heat for about 10 minutes.
Clean, peel and thinly slice the kohlrabi. Cut the cheese to the size of the kolrabi slices. Put 1 slice of cheese between 2 kohlrabi slices. Whisk the egg. Mix sesame and breadcrumbs.
Turn kohlrabi first in egg, then in the sesame mixture. Heat oil in a coated pan. Fry kohlrabi escalopes on each side over medium heat for 2-3 minutes. Wash basil, dab dry.
Set something aside for garnishing, cut the rest into fine strips. Season sauce again and stir in basil. Serve the kohlrabi schnitzel with the sauce. Garnish with basil.
Add the ciabatta bread.