Place the tofu between 2 pieces of kitchen paper and set a chopping board or other weight on top. Leave to stand for at least 10 minutes to remove excess water.
Remove the weight and kitchen paper, then cut the tofu into cubes.
Cook the noodles according to the packet instructions. Drain and set aside.
Mix together the cornflour, salt, pepper and five-spice powder in a bowl and use to coat the tofu. Heat 1 tablespoon of the oil in a wok or large frying pan over a high heat. Add the tofu and stir-fry for 2–3 minutes until golden. Remove from the pan and keep warm.
Heat the remaining oil in the pan, add the ginger and stir-fry for 1 minute. Add the noodles, stir in the soy sauce, chilli sauce and measurement water, then add the pak choi. Cook, stirring, until the leaves start to wilt.
Divide the noodles between plates and top with the tofu.