Spaghetti Sauce

1 pound ground beef
4 tablespoons vegetable oil, divided
1 small onion, finely chopped
1 (15 1/2 ounce) can tomato sauce
1 1/2 cups water
1/2 teaspoon pepper
1/2 teaspoon red pepper (optional)
1 (29 ounce) can tomato pur