Heat the oil in a wok, then stir-fry the meatballs for about 10 minutes, until they are golden brown all over. Add the Teriyaki sauce, soy sauce, rice vinegar and Mirin and coat the meatballs in the sauce until they are brown and getting sticky. Transfer them to a plate.
Now make the stir-fried vegetables.
Heat the oil in the wok and stir-fry the spring onions, garlic and ginger for 30 seconds, then add the the carrot pieces. Stir-fry for a minute, then add the greens, the teriyaki, soy, rice vinegar.
Stir-fry for a minute, then turn down the heat and let it bubble. After 3 minutes or so the vegetables should be tender.
Put back the meatballs, add the Mirin and sesame oil and warm through. Scatter the sesame seeds on top, then serve.