Cook the spaghetti in salted water until al dente, drain, reserve 100 ml of the cooking water, return the spaghetti to the pan, cover and set aside.
Heat the oil in a pan and fry the sausages and onions for approx. 1 min. Pour in the cream and reserved cooking water, simmer for approx. 3 mins. Stir in the rocket and cheese, season, mix with the spaghetti.