Step 1: Wash the kale and spin it dry in a salad spinner or shake it dry. Lay a leaf on a cutting board and making an elongated V-shaped cut, then remove the thick part of the stem. (You can leave the tender part of the stem near the top intact.) Repeat with the remaining leaves—you may not need to stem the tender inner leaves. Blot off any excess water with paper towels.
Step 2: Combine the sesame oil, soy sauce, and garlic in a small bowl and mix with a fork. Lightly brush each kale leaf on both sides with this mixture using a pastry brush. Sprinkle the kale on both sides with chopped peanuts and red pepper flakes.
Step 3: Set up your grill for direct grilling and preheat to medium-high. Brush or scrape the grill grate clean and oil it well.
Step 4: Arrange the kale leaves in a single layer on the grate (work in several batches as needed). Grill the kale until browned and crisp, 4 to 5 minutes per side, turning with tongs. Transfer to a platter and serve. I like to eat grilled kale with my fingers. It’s messy—it’s supposed to be, so provide napkins. Note: The kale should be plenty salty from the soy sauce, but don’t hesitate to add salt if you want to.