Place a wok on very high heat and add the sesame oil. Heat the oil until it just begins to smoke then add the cooked edamame. Stir to coat the edamame in the oil, then fry for 1 minute without stirring. Add the dried chilli flakes and fry for a further 2 minutes, stirring constantly to char all sides. Turn off the heat then add the soy sauce, continuing to stir until the sauce has evaporated with the residual heat of the wok.