Trim broccolini so that the pieces are no thicker than the green beans. In a large bowl, combine broccolini, beans, and kale.
Drizzle with oil and toss well to coat.
Heat a cast-iron frying pan or wok over medium-high heat until very hot.
Working in 2 or 3 batches, add greens mixture and cook until charred, 6 to 8 minutes per batch. Transfer to a large bowl and repeat with remaining vegetables.
Toss greens mixture with red pepper flakes and garlic, season with 1/4 teaspoon salt and a few turns of the pepper mill. Taste, and adjust seasoning, if needed. Devour.