Cook peas according to directions, drain well and hold aside. In heavy sauce pan saute' onion and parsley with two third of the butter (for about 5 minutes). Add rice and continue to saute' for 5 minutes. Add water and bring to boil, reduce heat, cover and simmer for 15 minutes. Stir peas, salt and remaining butter into rice. Place on a serving dish and add parmesan cheese.