Cook the rice according to the packet instructions. Put the porcini in a small bowl and just cover with boiling water to rehydrate them.
Meanwhile, peel the onion and cut into eighths, then place in a medium pan on a medium-high heat with 1 teaspoon of sesame oil. Cook for a few minutes, or until dark golden, stirring occasionally, while you peel and matchstick the ginger. Reduce the heat to medium-low, then add the ginger, miso paste and stock, along with the porcini and soaking water, leaving the last gritty bit behind. Cover and simmer gently for 20 minutes. Halve the radishes, put them into a bowl, toss in a splash of vinegar and a small pinch of sea salt and leave aside to quickly pickle.
Finely slice the chicken and tear the kale and nori into small pieces, removing any tough stalks from the kale. Break up the mushrooms, leaving the cute ones whole, and stir it all through the broth. Re-cover and cook for 4 minutes, or until the chicken is cooked through. Drain and divide the rice between your bowls, followed by the radishes. Season the broth to perfection, ladle it into the bowls, then serve.