They have gluten free buns that aren't listed on the menu. Just ask; they are $2. They also have meatless patties listed on the menu as GF.
I ordered a buffalo burger, which was delicious. They mixed up my GF bun with someone else's in my party, but the waitress caught it and made sure it was fixed without just switching the bun (they were cognizant of cross-contamination).
We somehow got an old menu and ended up getting overcharged by $1, but the manger fixed it and told her staff (in front of me) to fix the menus.
— Gluten-free items are marked on the main menu