When you get there, tell the server you have a food allergy, and would like to see your options. The chef will come out and see you and discuss what you can have and what you cannot. While we didn't eat at the River Belle, every single other location at Disney had many great gluten free options (and not just salads).
It is funny that the servers react instantly to the word "allergy", but they seemed to be confused if you say Celiac or Gluten free.
Weird hint, if you are having breakfast, be very careful with Bacon, as they drain it on white bread. Get it made special and you will be OK.
Also.. If you want a GREAT lunch sandwich, the Jolly Holiday has great GF sandwiches ( end of Main Street, on the left hand side). We did lunch here 3 times.