Heat oil in saucepan or skillet.Add onion;cook until soft.Crumble in the beef.Stir and fry until meat loses red color.Sprinkle with salt and pepper.Pour in tomato sauce and water;bring to boil.Break spaghetti;sprinkle in a little at a time,stirring into sauce and keeping it separated.Cover tightly.Simmer 20 to 30 minutes.Stir toward end of cooking time.Serve with cheese.Makes 3 to 4 servings.