Tassajara Cookbook by Edward Espe Brown is a great, simple cooking book. Its very light on specific recipes, and instead offers thoughts on ways to approach various vegetables, and general notes on preparing types of dishes (e.g. soups, casseroles, etc.) I love this one because it has revolutionized my cooking by breaking it down, and making me think about presenting the ingredients "as themselves" rather than trying to invent fancier and more complex dishes all the time.
Also by Edward Espe Brown are Tassajara Recipe Book (which was presumably written to compensate for the lack of recipes in the previous book) and Tomato Blessings and Radish Teachings. Of these, I like the second one better. It's got lots of short essays about things like mindfulness practice, and life in the monastery, and retains more of the spirit of the first book.
I am also enjoying 3 Bowls : Vegetarian Recipes from an American Zen Buddhist Monastery by Seppo Ed Farrey and Nancy O'Hara. This one is also full of wonderful little bit of Buddhist thought and practice, but the recipes are better organized than in the "Tomato Blessing" book.
There are others out there, including another one with "three bowls" in the title (which refers to practice of monks using three bowls at formal meals) but the three above are the ones I've used.
Eat mindfully :)