Put the noodles in a heatproof bowl, cover with boiling water and soak for 4–5 minutes, or until soft. Do not soak for longer or they may fall apart when stir-frying. Drain well.
Heat a wok or large frying pan with 1 tablespoon of the oil over a moderate heat. Pour the egg into the pan, swirling to make a thin omelette, then cook on one side for 2 minutes, or until almost cooked. Roll the omelette up gently and place on a chopping board. When cool enough to handle, slice thinly across the width of the roll, then set aside.
To make the sauce, mix all the sauce ingredients together in a bowl, then set aside until ready for use.
Heat the remaining oil in the wok, add the garlic and ginger and toss for 30 seconds until fragrant. Add the mince, breaking up any lumps, and cook for 4–5 minutes, or until the meat is cooked and slightly browned. Add the noodles, tofu and strips of egg and toss gently for 1 minute before adding the sauce and spring onions and heating through.
Turn the noodles onto a platter and sprinkle with the coriander, bean sprouts, peanuts and, if you are using it, the chilli. Serve while hot with lemon wedges.