Tip the rice into a bowl. Cover with cold water and set aside to soak.
Put the diced chicken leg in a bowl or dish. Add 1 tbsp cornflour and stir to evenly coat. In a separate bowl, stir together the tamari, 2 tbsp rice vinegar and 1 tbsp Demerara sugar (the sugar won't dissolve, so don't worry about that). Pour over the chicken and stir to coat. Set aside to marinate.
Put a wok or deep frying pan over a medium heat. Add the cashews and toast in the hot pan, shaking it occasionally, for 2-3 mins till the cashews are golden brown. Tip out onto a plate and set aside. Set the wok aside for later.
Peel and finely slice the onion. Halve the peppers. Scoop out the seeds and white bits. Finely slice the peppers into strips. Peel and grate the garlic and ginger. Finely chop the coriander stalks (keep the leaves for later).
Drain the rice and rinse it under fresh cold water. Tip it into a small pan. Pour in 400ml boiling water. Add a pinch of salt. Cover. Bring to the boil, then turn the heat down and simmer for 8 mins till the water has been absorbed. Take off the heat and leave to steam in the pan for 5 mins to finish cooking it. It will stay warm in the pan.
While the rice is cooking, put the wok back on the heat. Add ½ tbsp oil. Lift the chicken out of the marinade (keep the marinade for later). Add the chicken to the pan. Stir fry for 5 mins till browned all over. Lift out of the pan and pop on a plate.
Add the onion and peppers to the pan with 2 tbsp water. Stir fry for 4-5 mins till the veg start to soften. Add the chicken back to the pan. Stir in the garlic, ginger and coriander stalks. Stir fry for 1 min.
Add any marinade left from the dish. Pour in 150ml boiling water. Add the cashews. Cover and simmer for 5 mins to finish cooking the chicken all the way through.
Fluff the rice with a fork and divide between two warm bowls. Top with the chicken. Garnish with the coriander leaves.