Cook the udon according to instructions. When cooked, remove the noodles from the pan using a spaghetti claw. Retain the water. If you like, you can toss the noodles in a little vegetable oil to stop them from sticking, but if you work relatively quickly this isn’t necessary.
Stir around 150ml of the noodle water into the sauce ingredients. Stir to combine.
Return the noodle water to the hob over a medium heat and use it to cook the bok choi. If there’s not enough water remaining, top the pan up with some fresh boiling water.
Once the bok choi is cooked, drain the water off.
Add the noodles to the bok choi and mix. Add the sauce (as much or as little as you like.
Plate up the noodles. Top with the mince and sprinkle with peanuts and spring onion.