While Turkey is in the EU Customs Union, it does not have to abide by its laws unless it has specifically adopted the directive or regulation. This means that restaurants do not have to have information about allergens in their dishes in the same way as EU restaurants do.
That said, in the touristy and non-touristy places we visited, we found staff very friendly and willing to try to help. If you are staying in a resort, I dare say you can expect the same provision as anywhere else in the West, but even the small, local restaurants’ staff were willing to help.
Very few Turkish main courses use gluten routinely. So long as you avoid rice pilaf (which contains pieces of pasta), and have grilled meat and salads, it’s difficult to go wrong. And if you get tired of grilled meat, then falafel is available, if you feel you have a good communication channel going with a particular restaurateur.
In the summer in Turkey, the temperature can get very, very high. Temperatures around 45°C (115°F) are ruinous to normal ice cream. Thankfully, in Turkey there is an ice cream named Dondurma. When you try to buy it, the vendor may tease you by taking it away again, with a large stick (so don’t get upset!).
The presence of mastic in the ice cream keeps it almost-chewy instead of melting all over your hands and clothes. These ice creams are almost always gluten free.