Mix together the kingfish, soy sauce, sugar, sesame oil and sea salt and leave to marinate for 30 minutes. Use a slotted spoon to remove the kingfish.
Heat a wok until just smoking. Add the oil and, when hot, stir-fry the kingfish in batches until golden, then remove. Add the black beans, garlic and capsicum to the wok and stir-fry until fragrant. Deglaze the wok with s