I've cruised multiple times with Celiac and have always had amazing service.
When you get on-board go to the main dining room and talk to the head waiter (you can call prior to the cruise and have your reservation noted) and have them take down your name and cabin number.
For dinner, the head waiter will come by and give you the menu for the following night and have you pre-place your order so it can be prepared in a separate kitchen. If you're going to a specialty restaurant the next night, just tell them and they will make sure the head waiter at that restaurant knows.
For breakfast and lunch I've always had the head waiter spot me and come over to take my order. Head waiter becomes your best friend. If there's something you want and don't see - ask. Many times they will make it happen. I've had all kinds of things - cake, breakfast items, even a specialty item unavailable in the main dining room. Key is to make friends with the head waiter, your waiter, and your assistant.
I had less luck in the Windjammer. Again, find the head waiter and they will get the chef for you. I try to avoid Windjammer.
In main dinning room you can also ask to be seated with the same wait staff every evening even with MyTime Dining.