Seitan is a meat substitute made from wheat gluten. It's made by creating a simple dough which is then put through a process of rinsing in water repeatedly to remove the starch but keep the gluten. It's often used as a meat-free alternative in Japanese and Chinese dishes.
Start by making the sauce, tip half the beans into the bowl of a food processor with the rest of the ingredients and add 50ml water. Season, then blend until smooth. Pour into a saucepan and heat gently for about 5 mins or until thick and glossy.
Drain the seitan and pat dry with kitchen paper. Toss the seitan pieces in a bowl with the cornflour and set aside. Heat your wok to a high temperature, add a little oil, then the seitan – you might need to do this in batches. Stir-fry for around 5 mins until golden brown at the edges. Remove the seitan from the wok using a slotted spoon and set aside on a plate.
If the wok is dry at this stage, add 1 tsp vegetable oil. Add the shallots and stir-fry until soft. Throw in the chopped peppers, the rest of the beans, pak choi and spring onion. Cook for 3-4 mins, then return the seitan to the pan, stir in the sauce and bring to the boil for 1 min. Serve with cooked rice or noodles.