Cut the chicken into bite-sized pieces and put them in a small bowl. Add half of the sesame oil, soy sauce, Mirin and rice vinegar. Combine, then rest for at least an hour.
Heat a wok, then add the marinated chicken, sugar, garlic, ginger and sesame seeds. Stir fry for 5 minutes until the chicken has changed colour.
Add the green beans and the remaining soy sauce, Mirin, rice vinegar and sesame oil. Stir-fry for about 5 minutes, until the chicken and beans are cooked through and they are slightly sticky.
Add the spring onion and the remaining sesame seeds. Stir-fry for a minute to combine.
Meanwhile, cook the noodles in another pan according to the packet instructions, then drain and keep warm.
When the chicken and beans are ready, add the noodles and combine.
Serve warm