Pop the water, two of the spring onions, the garlic and the fine salt into a large saucepan and set over a high heat. Bring to the boil, then throw in the chicken breasts. Bring back to a simmer, pop the lid on and turn off the heat. Leave untouched for 25 mins, the residual heat will cook the chicken through. Then using tongs, remove the chicken from the liquid and set aside to cool.
Meanwhile finely slice the remaining spring onions and celery. Roughly chop the coriander and ¾ cucumber, thinly slicing the rest for garnish.
Once the chicken is cool enough to handle, shred into pieces using two forks. In a bowl, add the chicken, miso, mayonnaise and tahini, mixing well until evenly coated. Then fold through the ¾ of the chopped spring onions, celery, coriander, cucumber and sesame seeds, until thick, creamy and scoopable. Season with black pepper and a little salt if needed.
Heat the rice and divide between bowls. Add a dollop of the chicken mixture with the sliced cucumber, remaining chopped spring onions and a drizzle of crispy chilli oil to finish.
