Cook the spaghetti in boiling salted water for about 10 minutes. In the meantime peel and chop the onions. Peel the sausage skin. Dice the sausage as well. Whisk eggs with milk. Season with salt and pepper.
Drain the spaghetti and let it drain. Heat 1 tablespoon of oil in two pans. Fry 1/4 of the onions and the sausage in each pan. Add 1/4 of the spaghetti and pour 1/4 of the egg milk over each.
Let it falter at low heat. Push together from the centre to the edge to form a semicircle. Turn over with a spatula, allow to set from the other side and keep warm for a short time. Prepare 2 more omelettes from the rest.
Prepare the tomato sauce according to the instructions on the packet. Arrange omelettes on 4 preheated plates. Place a dollop of tomato sauce on each plate. Garnish with gherkin slices, tomato quarters and parsley.