Barcelona has some good choices for vegetarians. Although I'm not sure if it's typical Catalonian fare, we enjoyed these restaurants:
Juicy Jones: Fantastic fresh juice. Don't be misled by the small entrance, there's a restaurant a few steps below just past the juice bar. We tried a variety of small plates for a very reasonable price. Nothing exceptional, but you get to try lots of things.
Terrablava: This buffet restaurant was heaven-sent. We were craving good veggies, and the salad bar served em up, as much as we wanted. There's also cheese (and meat) pizza and pasta. It's apparently very busy during the day with business people, but in the evening it's pretty empty. And how can you beat all-you-can-eat when you're backpacking?