Put a large pan of water on to boil
Peel and finely slice the ginger and garlic and finely slice the chilli. Slice the chicken into finger-sized strips and lightly season with salt and pepper. Cut the ends off your spring onions and finely slice. Pick the coriander leaves and put to one side, and finely chop the coriander stalks. Halve the bok choi lengthways. If using the mushrooms, either tear into pieces or leave whole.
Preheat a wok or large frying pan on a high heat and once it’s very, very hot add a good lug of groundnut oil and swirl it around. Stir in the chicken strips and cook for a couple of minutes, until the chicken browns slightly. Add the ginger, garlic, chilli, coriander stalks, mushrooms (if using) and half the spring onions. Stir-fry for 30 seconds, keeping everything moving round the wok quickly. Add your noodles and bok choi to the boiling water and cook for 2 to 3 minutes, no longer.
Meanwhile, add the cornflour, water chestnuts and their water to the wok and give it another good shake to make sure nothing sticks to the bottom. Remove from the heat and stir in 2 tablespoons of soy sauce. Halve the lime, squeeze the juice of one half into the pan and mix well. Drain the noodles and bok choi in a colander over a bowl, reserving a little of the cooking water. Stir in the noodles and bok choi, with a little of the cooking water to loosen if necessary, and mix well. Have a taste and season with more soy sauce if needed.
Use tongs to divide everything between two bowls or plates, or to lift on to one large serving platter. Spoon any juices over the top and sprinkle with the rest of the spring onions and the coriander leaves. Serve with lime wedges.