Most, if not all, of the Lebanese restaurants will be able to do a vegetarian plate for your guests. My favourite is Ali Baba's, which consists of felafel, hummus and tabbouleh with homemade flatbread...yummy!
In addition, almost every Chinese place I've visited has been more than willing to make me a (most times huge!) veggie stir fry even if it wasn't listed on the menu board.
One thing to be careful about is that many restaurants use lard for frying. If your guests are really serious about not eating any dead animal products, they'll want to ask.