Mix all the sauce ingredients in a small mixing bowl and set aside.
Cook the Udon Noodles
Add the noodles to a pot of boiling water stir gently for 1-2 minutes or until the udon noodles are separated.
Now, rinse the noodles then and drain them under cold water.
Heat a large pan over medium-high heat and add the oil.
Stir in the ground beef, fry for 1-2 minutes, then add mushrooms, spring onion and bok choy, cook for 2 to 3 minutes.
Add in the noodles and the sauce. Cook for 3 minutes more, then serve.
If you're substituting seafood for beef (check recipe variations further in this blog), keep the prepared fish aside while stir-frying the vegetables. Add them back in with the udon noodles after that.
Start with the one that takes the longest to cook while preparing the vegetables. As a result, each vegetable will be cooked to perfection.
To untangle the strands of udon noodles before stir-frying, quickly rinse them under running water. Fresh udon noodles are vacuum-sealed when they come in a plastic bag. They need to be run under water beforehand or become knotted and difficult to disentangle while stir-frying.
Warm the udon noodles in boiling water before rinsing if they are cold from the fridge. Cold udon noodles take time to warm up while stir-frying, as the other ingredients become overcooked.
Don't be intimidated by dealing with noodles in a stir fry. Pre-cooked udon noodles are easy to reheat and are ideal for putting a dish together. The noodles just take a few minutes to heat up and can be tossed right into the skillet with the vegetables, and sauce.