Cook noodles as directed on package and drain. Set aside. Brown ground beef and onions. Drain fat. Mix all ingredients together except nuts or chow mein noodles used for topping. Pour into large casserole or 9 by 13 inch pan.
Bake at 375 degrees for 40 minutes. While baking crush chow mein noodles slightly or measure and set aside nuts.
Remove casserole from oven. Sprinkle with chosen topping. Return to oven for 10 minutes more.