Peel and grate the shallots, garlic and ginger. Put them all in a mixing bowl. Stir in 1 tbsp rice vinegar, 2 tbsp of the tamari and a pinch of chilli flakes to make a marinade.
Slice the mini chicken fillets into pieces that are all roughly the same size – about 2 cm long. Add to the marinade. Stir to mix. Set aside to marinate for 15 mins.
Tip the rice into a small pan. Pour in 400ml boiling water. Add a pinch of salt. Cover. Bring to the boil. Turn the heat right down. Very gently cook for 20-25 mins till all the water is absorbed. Take off the heat. Set aside, lid on, for 2-4 mins till the rice is cooked.
While the rice cooks, trim and finely slice the leek. Halve the peppers. Scoop out the seeds and white bits.
Slice into long lengths.
Warm 1 tbsp oil in a deep frying pan or wok. Add the leek and pepper. Stir fry for 5 mins till the veg are soft and glossy.
Add the chicken and its marinade to the wok. Stir fry for another 5 mins till the chicken is browned all over. Add 200 ml boiling water to the wok. Cover and simmer for 10 mins till the chicken is cooked through.
Tip the sesame seeds into a dry frying pan. Toast over a medium heat till the seeds are golden brown and smell nutty. Shake the pan every so often to stop the seeds sticking. Take off the heat.
Add the spinach to the chicken and stir till it wilts. Taste the stir-fry and add more tamari if you think it needs it. Sprinkle over the sesame seeds and serve it with the rice.