Heat oil in a 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.
