There are not a lot of vegetarian choices in Avignon. Indeed, most restaurants do not even offer a vegetarian option, much less a vegan option. Terre de Saveurs advertises itself as offering "traditional and vegetarian cuisine," and compared to most vegetarian restaurants throughout the world, the pickings here are rather slim.
On the other hand, they do offer a bunch of vegetarian items, along with some vegan items, and the food is very good and healthy. The service is not great, and this place is not inexpensive. But if you are in Avignon and are a vegetarian or vegan, this place is quite a find.
If you want to find another place nearby, a few things to consider: (a) Zocalo is closed. (b) 5 Senses is not vegan, and very expensive (I did not eat here--5 Senses is a fancy high quality restaurant that offers a vegetarian option, and so if you are not vegan and have plenty of $$$ you might check it out). (c) Some restaurants in Avignon list their fish dishes as vegetarian items--so be alert! (c) There is an organic restaurant called Naturabsolu in nearby Villeneuve Avignon. They were closed when I got there, but my understanding is that they prepare one meal per day, and the meal might (or might not) be vegetarian, so you might want to call in advance.
Cons: not inexpensive, not great service