Peel, rinse and finely slice the onion. Place it in a pan with the oil and fry until soft, add the peas, sauté for a minute then cover them completely with boiling water. Add a pinch of salt and a grind of pepper, cover the pan and simmer until the water has almost evaporated and the peas are cooked.Season with salt and pepper to taste. In the meanwhile cook the pasta in plenty of boiling salted water. Drain it al dente, toss it in the pan with the peas, sauté and pour it in a serving dish, sprinkle with chopped parsley and serve.