Preheat the oven to 160C/fan 140C/gas mark 3. 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 e 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 snap peas, fry for one minute then move to one side of the pan. Add the rice and drained peas to the other side of the pan. Fry for two minutes.
Make the dressing by whisking all the ingredients together. Add more of each element depending on taste.
Divide the rice and peas between two serving bowls. Add the carrot, radishes, spring onions, coriander and pak choi and sugar snap peas, then pour over the dressing.
Remove the fish from the oven. Add to the dish and drizzle over any juices.