Peel and grate the shallots, garlic and ginger. Pop them all in a mixing bowl. Stir in 1 tbsp rice wine vinegar, 1 tbsp Demerara sugar, 2 tbsp of the tamari and a pinch of chilli flakes.
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. Fill the kettle and boil it.
Tip the rice into a small pan. Pour in 300ml hot water from the kettle. Add a pinch of salt. Cover. Bring to the boil. Turn the heat right down. Simmer for 20-25 mins till all the water has been absorbed. Take off the heat. Steam, lid on, for 2-4 mins till the rice is cooked.
While the rice cooks, trim the leek. Rinse it and finely slice it. Rinse the pepper and halve it. Scoop out the seeds and white bits. Slice into long lengths.
Warm a little oil in a deep frying pan or wok. Add the leeks and pepper. Stir-fry for 5 mins till the veg have softened and look glossy. Fill the kettle and boil it.
Add the chicken and its marinade to the wok. Stir-fry for another 5 mins till the chicken is browned all over. Add 200ml hot water form the kettle to the wok. Pop on a lid. 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.
Rinse the spinach. Add to the chicken. Stir it in so it wilts. Taste the stir-fry and add more tamari if you think it needs it. Serve with the rice, sprinkled with the sesame seeds.