This is a go-to. I get a lettuce wrapped burger. I let them know it's an allergy so they don't put the sauce on it either. The only thing that goes in the fryer is the French fries so they are safe. I've never gotten sick and I've ate at this specific location many many times.
Just let them know it's an allergy and they will wrap it separate of anybody else's.
— Very
— No gluten-free information on the menu
— Some
— Excellent