There are very few vegetarian friendly sandwich shops out there, but Capriotti's is one of them. They have a handful of sandwiches made with faux meats. The sandwiches they make are also quite filling. Their small is a 9 inch sub, with a 12 inch, and an 20 inch sub rounding out the options.
Edit: I was recently informed that the faux meats that Capriotti's has are NOT vegan. Sorry if my previous review led anyone astray.