Heat pan on medium high heat, and add oil.
Stir-fry onion until soft, and add beef/pork.
Stir-fry until no longer pink.
Remove and set aside.
Add udon noodles, and 2 tbsp water.
Gently break up noodles, and add carrot.
Then add in beef and onions, and pour in sauce mixture.
Add cai xin, and toss everything together to combine.
Remove from heat when cai xin is wilted.
Serve garnished with chinese parsley.