Fordes do very good vegetarian dishes but they are a bit pricey and booking is generally essential. Try and get in for the early bird prices up to about 7.30. The Mukhut is a excellent Indian restaurant which does a good selection of veggie food, there's Robertinos (Italian) but having eaten there once or twice I can't say I was that impressed. You will find most places have at least one or two veggie options on the menu, during the day it's worth checking out the cafe in the Westgate ( gift shop with a large canteen style cafe in the basement) - I 'd particularly recommend the basil and cheese baked potato!
In our family there is one vegan, one vegetarian and one fish but no meat eater and it's become much easier to eat out the last couple of years.
There's also a couple of Healthy Food shops ( Only Natural and Only Natural too) which sell veggie snack foods.