Enchilada Bake

(Grandma Pauline)
1 lb. Hamburger
1 small onion
1 (15 oz) can tomato sauce
1 (14.5oz) can diced tomatoes
1 can green chilies
1 pkg. corn tortillas
1 pkg. enchilada or taco seasoning
½ lb. grated cheese
Layer in pan and bake at 350* for 25 minutes