Rinse the bean sprouts and chives and drain well. Heat a wok until just smoking. Add the vegetable oil and, when hot, stir-fry the ginger and garlic until fragrant, about 30 seconds. Add the bean sprouts and chives and stir-fry until just limp, then add the soy sauce, sea salt, sugar and stock and cook for another minute. Stir in the coriander leaves to serve.