Brown hamburger and onion in a large skillet. Drain grease off the meat.
Add enchilada sauce and refried beans. Simmer for 5 minutes.
Meanwhile, crush tortilla chips and grate cheese.
Assemble casserole in a 9 by 13 pan. Start by layering half the bag of chips, followed by half the meat mixture and half the shredded cheese. Repeat the layers, ending with cheese on the top. Bake at 350 degrees for 20 minutes.