Cut the onion and pork belly into small cubes and the cabbage into fine strips. Heat the rapeseed oil in a large, non-stick pan. Steam the onions in it until translucent, add the bacon and fry until crispy. Add the cabbage and don`t fry too soft.
Put the spaetzle in the pan with a little water. Stir again and again until the water has evaporated and the spaetzle are lightly browned. Season with plenty of fresh pepper and possibly some caraway seeds. Chop the parsley and sprinkle over the spaetzle just before serving.
If you want it a little creamier and richer, you can achieve this with a tablespoon of sour cream or a dash of cream or stir in some grated Emmentaler.