Mix the sauce

• Combine the soy sauce, oyster sauce, brown sugar and sesame oil in a bowl.
• Stir until the sugar dissolves.

Cook the udon

• Boil the udon noodles until tender, then drain and rinse.

Sear the beef

• Heat the vegetable oil in a wok over high heat.
• Add the beef and sear until browned, then set aside.

Stir fry the vegetables

• Add the garlic, ginger and onion to the wok and fry until fragrant.
• Add the bell pepper and bok choy and stir fry until just tender.

Combine everything

• Return the beef to the wok with the udon noodles.
• Pour in the sauce and toss until everything is coated and hot.

Serve

• Top with sesame seeds and spring onion.