I recommend any of the Tasajara cookbooks from the San Francisco Zen Center:
This one is a compendium of entries from multiple books: https://www.amazon.com/Complete-Tassajara-Cookbook-Techniques-Reflections/dp/1590308298
The recipes are simple, tasty, and very frugal. They were developed at the San Francisco Zen Center's mountain retreat so they needed to be practical.
I also recommend anything by Madhur Jaffery, especially her Vegetarian India and her World Vegetarian.
https://www.amazon.com/Vegetarian-India-Journey-Through-Cooking/dp/1101874864
https://www.amazon.com/Madhur-Jaffreys-World-Vegetarian-Meatless/dp/0609809237
Her non-vegetarian cookbooks / recipes are also great as well!
What makes both Tassajara and Madhur Jaffery so good is that it is clear that they cooked the recipes multiple times themselves and really practiced them to get the recipe right. I also really like Meera Sodha from The Guardian for the same reason, but I sometimes find her recipes a bit too fancy. But when they are good, they are very good.