Place the chicken thigh skin-side down horizontally and make shallow cuts vertically. Cut in half and place in a plastic bag. Add the seasoning ingredients (sake, sugar, miso, grated ginger) to the bag, massage well, and refrigerate for 15 minutes.

Cut the green onion into 4cm lengths, make shallow cuts, remove the center, and slice thinly. Soak in water for 5 minutes, then drain. Cut the bok choy in half and slice the root into quarters vertically.

Boil water in a pot, add the bok choy, and cook for 2 minutes. Drain thoroughly.

Heat salad oil in a frying pan over medium heat. Add the marinated chicken and cook for 3 minutes. Flip, cover with a lid, and steam-fry for another 3 minutes.