Guacamole and Beef Casserole

1 lb. ground beef
1 small onion
1 (5.3 oz.) can evaporated milk
1 pkg. dry enchilada spice mix
1 (10 oz.) can cream of mushrooms soup
1 (4 oz.) can chopped green chilies
Tortillas chips
3 C. shredded cheddar cheese
Sour cream and guacamole (optional)

Preheat oven to 350 degrees F. Brown ground beef and onion in a skillet, stirring until ground beef is crumbly. Drain. Stir in milk, enchilada spice mix, soup, and green chilies. In a 9 x 13 inch baking pan, make 2 layers of chips, ground beef mixture, and cheddar cheese. Bake for 30 minutes. Serve with sour cream and guacamole, if desired.