If you add garlic to your guacamole, we have bad news: You’re not doing it right. Do you mince the onion? That’s also a no-no. And, please, leave the avocado lumpy.

So says 97-year-old Diana Kennedy, a foremost authority on traditional Mexican cuisine. Over many decades, she has mastered, documented and become fiercely protective of the culinary styles of each region.

This summer, a portrait as zesty as her dishes come in the form of the documentary “Read Full Story