Tip the rice into a sieve and give it a good rinse under cold water. Tip into a small pan and add 300ml boiling water and a pinch of salt. Pop on a lid and bring to the boil, then turn right down and very gently simmer for 8 mins, till all the water has been absorbed. Take the rice off the heat and leave it to steam in the pan, covered, for 10 mins.
While the rice cooks, halve the chilli, flicking out the seeds and pith for less heat, and finely chop it (this week’s chillies are HOT, so even if you like things spicy, be sure to flick out all the white bits and have a nibble to see how much you want to add – half may be plenty). Peel and grate the garlic cloves and ginger. Finely chop the coriander stalks. Grate the lemon zest. Slide everything into a mortar and pestle (or use a small bowl and the bottom of a jar) and add 1 tsp tamarind, 1 tbsp sugar and a good pinch of salt and pepper. Bash till the ingredients come together to make a rough paste.
Trim the ends off the French beans. Slice the chestnut mushrooms.
Bring a large frying pan or wok to a medium-high heat and add 1 tbsp oil. When hot, add the diced chicken leg and stir fry for 5-6 mins, till golden on all sides and cooked through. Scoop out of the pan with a slotted spoon and transfer to a plate.
Slide the beans and mushrooms into the now empty pan. Fry for 3-4 mins, stirring frequently, till browned. Return the chicken to the pan and pour in the paste from the mortar and pestle. Stir fry for a further 2 mins.
Fluff up the basmati rice and pile onto plates. Serve the stir fry spooned over the rice, finished with a scattering of torn coriander leaves and wedges of lemon for squeezing.