In a heavy saucepan bring lentils salt and 4 cups water to a boil Cover and simmer 20 minutes or until the water is absorbed and the lentils are tender Meanwhile brown beef in a skillet Drain excess fat Stir in soup mix catsup mustard vinegar and remaining water Gently stir in lentils Spoon into a 2-quart casserole Bake covered at 400 for 30 to 35 minutes Yield 4 to