Heat wok & add both peanut oils. When hot, add garlic, ginger, red pepper flakes & scallions. Stir-fry 30 seconds, then add greens & stir-fry for 1 more minute. Add vegetable stock, cover & steam until tender, 2-3 minutes. Season with salt, sesame oil & mirin.
Lift greens with tongs and set on serving platter. Add the cornstarch to the juices left in the wok & boil until thickened. Pour the sauce over the greens & serve.
Serves 4