Thoroughly wash the water spinach, discarding any wilted leaves and coarser stalks. Tear or cut into 10cm/4in sections. Snip the chillies in half or into 2cm/¾in sections, discarding the seeds as far as possible.
Heat the oil in a wok until hot but not smoking. Add the chillies and Sichuan pepper and stir-fry for 10–20 seconds until the oil smells spicy and the chillies are just beginni