Before I went gluten-free, I never ate at fast food restaurants. After going G-F I learned about In N Out Burger.
This quick serve restaurant not only has relatively high quality and tasty food, it doesn't serve any bread-y fried foods (i.e. chicken), so the french fries can't be cooked in oil that is contaminated with gluten (as confirmed by at least one FTN test). Also, you can order your burgers "protein-style", and if you tell them that you have a gluten allergy, then they note that in your order and allege to take special precautions regarding cross-contact from buns, etc. Check-out how the receipt below identifies gluten to the food staff!