Prepare the spaetzle in boiling salted water according to the instructions on the packet. Cut Cabanossi into slices. Clean, wash and cut the peppers into strips. Clean and wash the mushrooms. Peel onions and cut into slices.
Heat the oil in a pan. Fry the sausage and vegetables for approx. 3 minutes, turning them over. Fold in spaetzle. Whisk eggs and milk. Season to taste with salt, pepper and nutmeg. Grease 4 casserole dishes (each with a capacity of approx. 300 ml or 1 large dish) and distribute the spaetzle mixture in the dishes.
Sprinkle with egg milk and sprinkle with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Garnish with parsley.