I recently had dinner at Tartinery in Nolita and found a great vegan option on their menu. A ratatouille open faced sandwich, or tartine, on sourdough bread. It's everything you expect from ratatouille with a nice addition of crusty bread and fresh herbs.
The restaurant has a great vibe. Glossy black pendant lights, chalkboard walls + lots of exposed brick and wood.
They also have a vegan Gazpacho and several salads that can be veganized - and fresh juices until 6pm. (Don't be late - they disassemble the juicing machine at 6 sharp).