Peel onions and cut them into fine rings. Clean and wash spring onions and peppers and cut them into rings. Clean, wash and quarter the tomatoes and remove the seeds. Cut the flesh into small cubes. Put Maultaschen in 750 ml boiling broth and let it simmer at low heat for about 20 minutes.
In the meantime heat oil in a pan, fry onion rings, bell peppers and spring onions in it while turning. Season with salt and pepper. Deglaze with the remaining stock and cook over medium heat for about 10 minutes. Then season again with salt, pepper, sugar and vinegar. Add the tomatoes. Keep warm. Lift the Maultaschen out of the stock and let them drain briefly. Heat the fat in a frying pan and fry the Maultaschen briefly on each side. Arrange two Maultaschen and half the vegetables on a small plate.
Add the tomatoes. Keep warm. Lift the Maultaschen out of the stock and let them drain briefly. Heat the fat in a frying pan and fry the Maultaschen briefly on each side. Arrange two Maultaschen and half the vegetables on a small plate. Serve garnished with lamb's lettuce as desired