I don't have any books in mind for simple vegetarian foods, but if you're looking to venture out one day, there's a lot of good vegetarian Indian cookbooks.
For simple stuff, I'd look up Asian stirfry recipes using temphe or tofu. Seventh Day Adventists (most of them are vegetarian) websites would have some recipes, and I know they have cookbooks too (I was raised 7th day adventist).
II make stir fry all the time, it's quick, tasty, healthy. The longest thing to cook is the rice.
