Finely chop the onion and sauté with the diet margarine until translucent. Squeeze out the sauerkraut, add to the onions and cook for 4-5 minutes. Season to taste with salt, pepper and caraway seeds.
Preheat the oven to 200 °.
Brush the ham slices with mustard, cover with the sauerkraut and onion mixture and roll up tightly. Place in a greased dish. Place a slice of cheese on each roll, pour in the vegetable stock and bake in the oven for about 20 minutes.