Preheat the oven to 160°C. Mix the miso and soy sauce together.
Put the mackerel skin side down on a piece of foil on a baking tray. Brush it with the miso mixture, then wrap in the foil and put in the oven for 10 minutes.
Meanwhile, heat the oil in a frying pan. Add the pak choi and sugar snaps, fry for one minute, then add the rice and drained peas. Fry for two more minutes.
Make the dressing by whisking all the ingredients together. Add more of each element depending on taste.
Divide the rice between two serving bowls. Add the carrot, radishes, spring onions and coriander, then pour over the dressing.
Remove the fish from the oven. Add to the dish and drizzle over any juices.