Santorini’s has a decent list of options on their gluten-free menu. in fact, the GF menu is two pages long!
as far as classic Greek foods go, they had 2 gyro options that were gluten-free: chicken or veggie. however, without the pita bread, it’s not quite the same. so you might want to bring along some gluten-free bread with you. the tzatziki sauce is safe to eat, thankfully, as I feel like it makes the dish. however, if you have a dairy allergy, this is not the option for you.
there were several other sandwiches and burgers, for which you may want to bring bread if you think you my want to order one of them.
I tried the souvlaka, which was like steak kabobs. it was a generous amount of steak, and the grilled onion and peppers were the perfect complement.
some of the other options I was trying to decide between were the prime rib (it states that we can have the au jus, which I thought was odd, so double-check that if you order it), various steaks, lobster, pork chops, or walleye.
they even had two gluten-free pasta dishes on the menu (spaghetti arrabbiata and cajun pasta)
I was surprised at how packed the restaurant was, so if you plan to go (particularly on a weekend), try and make reservations.