The night before prepare the marinade by mixing mirin, soy sauce, rice vinegar, fresh grated ginger, pressed garlic, red chilli flakes and honey in a wide and shallow bowl. Add the beef strips, mix well, cover with plastic wrap and refrigerate until the next day. Alternatively, you can marinade the beef for 1 hour if you are short on time.
Before starting on the stir fry cut and slice all vegetables and have them ready to go.
Heat a large pan or a wok over medium high heat, add the vegetable oil. Take the beef out of the marinade and brown over high heat for 1-2 minutes on each side. Do it in batches to avoid overcrowding and steaming. (Reserve the marinade, you should have approximately ⅔ cup/175 ml of marinade.) Once the beef is seared, put it in a clean bowl and set aside.
To the same pan add sliced red onion and stir fry oven high heat for 3 minutes until it’s got a bit of colour on it but still crunchy.
Return the beef to the pan with the reserved marinade, beef stock and bring to a simmer, then add the cornstarch diluted in water and stir until thickened, continue simmering for 5 minutes, then add sesame oil, green onions, stir to combine and take it off the heat. Serve sprinkled with sesame seeds and sticky white rice or noodles.