Preheat oven to 400 degrees. Thaw pie crust 10 minutes. Prick bottom and sides of pie crust with fork. Bake pie crust for 10 minutes. Remove from oven and reduce temperature to 350 degrees.
In skillet, brown hamburger and onion until brown. Drain fat. Add taco seasoning mix. In small bowl, combine refried beans and 1/3 cup taco sauce.
Layer 1/3 of refried bean mixture into pie crust; cover with 1/2 hamburger mix, then 1 cup cheddar cheese and crushed nacho chips. Repeat layers, except nachos. Bake an additional 20-25 minutes. Remove from oven. You may top with lettuce, tomato and additional taco sauce or sour cream. My family likes it without.