I used to go through the hassle of calling ahead, but I have learned that it is not necessary. As long as you aren't a terribly picky vegetarian, there is plenty to choose from - without making special arragement. WDW is one of the few places I enjoy eating out because I typically have CHOICES of well prepared, nicely seasoned food. I've been a vegetarian my whole life (39 years) and in the past 10 years or so many restaraunts have begun to offer one, maybe two vegetarian options - but they usually aren't very good. For some reason many people think Vegetarians like bland food - not me! All of the restaurants have at least one vegetarian entree - just ask if you don't see if on the menu.
As mentioned - Boma is GREAT. I typically do not like any type of buffet, but I could eat about 2/3 of the items on the buffet, and everyone of them was wonderful. I also have had good luck ordering Portobella mushrooms at the "steak houses" (Canada's restaurant and WL's steak house - can't remember their names). The mushrooms come nicely seasoned and well presented. It's fun to put steak sauce on them. The first time I got a mushroom like this at WL's restaurant, my husband tried to send it back - he thought it was a steak!
Finally - my favorite meal is at the Rose and Crown - they have a mushroom appetizer which they make into a meal size portion for me. It is a variety of mushrooms in a cream sauce served over a biscut. I know it must have a gazillion calories because of the cream sauce, but it is SOOOOOOO good!
Enjoy all the choices and great food!!
Morganne's Mommy