Heat the oil in a wok and add the spring onions and red onions. Cook over a high heat for 3-4 minutes until well browned.
Meanwhile, heat the rice according to the instructions on the packet. Add to the pan with the mirin, soy sauce, ginger and green beans, and cook for 2 minutes.
Stir in the pak choi and beef, and cook for 3-4 minutes until piping hot.