Two books come to mind. The first is: The Food Matters Cookbook - 500 Revolutionary Recipes for Better Living by Mark Bittman.
This book IS a recipe book, but Mark, as usual in his writing, offers lots of alternative and variations which make it especially good for inspiration. The author had some health issues which turned him to this healthier approach to food, but he knows what good food is and he doesn’t leave flavor behind just to make thing healthier.
The second I believe may be just what you asked for a book about cooking, without too many recipes. It is: An Everlasting Meal – Cooking with Economy and Grace by Tamar Adler.
In the Forward Alice Waters writes “. . . a book grounded in instinct, prompting the reader to examine the world around him- or herself differently, allowing cooking to become a continuous, integrative process that flows from meal to meal.”
And in the introduction Tamar states: “This is not a cookbook or a memoir or a story about one person or one thing. It is a book about eating affordably, responsibly, and well, and because doing so relies on cooking, it is mostly about that.”
This is not a health food book, but it is full of healthful ideas.