The Food Court here is well stocked, but beware... it can get very busy at weekends and dinner times so seats may not be available.
A favourite of mine is Panchos, although the vegan and vegetarian options are limited, the owner knows his stuff! Home made guacamole, veggie fried rice, optional cheese, real Mexican ingredients and veggie sides make it a must go. (you can also get some nice Mexican beers or tequila with your meal)
There are also a couple of Middle Eastern and Mediterranean cafes that serve large portions of mixed salads, falafel sandwiches, stuffed vine leaves, pittas, and hummus. I've never eaten at the other stalls but seen some veggie options, the Queen Brie also specialise in vegetarian cheeses and local produce such as chutneys, wine, crackers and hampers.