Heat the oil in a pan and fry the chicken fillets for 5 minutes on each side, season, remove from the pan.
Melt the butter in the frying oil, fry the spaetzle and cabbage in it for about 5 minutes and then season. Sweat the flour in it. If you like, you can take out the spaetzle and cabbage beforehand, then it works better for me with the roux. Deglaze with stock and cream, bring to the boil and then simmer for about 2 minutes.
Put the spaetzle mixture in a baking dish, cut the chicken fillets into bite-sized pieces, add to the mixture, sprinkle cheese on top and then put in the oven.
Bake at 200 degrees for about 12-15 minutes, then sprinkle with parsley and fried onions.