Meanwhile, heat vegetable oil in a large, deep frying pan or wok over high heat. Add mince and cook, breaking up lumps with a wooden spoon, for 5 minutes or until browned.
Add noodles to beef and cook for 2 minutes or until noodles have separated. Add sauces, sugar and sesame oil, then cook, stirring, for 1 minute or until heated through.
Meanwhile, add beans and choy sum to saucepan, then cook for 1 minute or until just tender. Drain. Add to beef mixture with half the onion, then toss to combine. Divide beef mixture among bowls and serve topped with cashews and remaining onion.