Thoroughly mix together the cornflour and the egg white in a medium bowl.
Cut the chicken breast into strips 3-4mm (⅛") thick and add them to the egg white and cornflour mix, then set aside whilst you prepare the vegetables.
Top and tail the red onion, cut it in half, peel it and then cut it into slices (top to bottom) 5-6mm (¼") thick.
Peel the garlic and slice it as finely as you can.
Peel the ginger and grate it.
Top and tail the sugar snap peas and then cut them into strips at a 45° angle, 3-4mm (⅛") thick.
Remove the stem and the seeds from the chilli then cut it into strips as thinly as you can.
Remove any tough outer leaves from the spring onions and then cut them at a 45° angle into pieces 3-4mm (⅛") thick.
Cook the udon noodles as per the packet instructions and refresh them in cold water. I use straight-to-wok noodles that just need to soak in boiling water for a few minutes and then separate them.
Mix together the soy sauce, Chinkiang vinegar, sugar and msg and set aside.
Heat a wok over a high heat and when it is shimmering, add the cooking oil. Remove the chicken from the egg mixture and then carefully add it to the oil and stir fry for 1-2 minutes, then remove and place on kitchen paper.
Pour off all but a scant coating of oil and then return the wok to a high heat, when the wok is hot again add the red onion and stir fry for 1 minute.
Throw in the garlic, ginger, spring onion, sugar snap peas and bean sprouts and stir fry for 1 minute.
Pour in the soy sauce mix followed by the chicken and stir everything to coat, no more than 1 minute.
Add the noodles, and chilli and stir fry until hot, again around 1 minute should be fine.
Serve sprinkled with the green parts of the spring onion, pickled ginger, sesame seed and coriander leaves.