Slice the chicken into strips and place in a bowl. Season well with salt and pepper.
Grate the ginger and garlic into a bowl. Use around a tablespoon of the mixture to add to the chicken. Marinade the chicken for half an hour (optional)
Add the Gochujang, Gochugaru, Corn Syrup, Mirin, Light Soy Sauce, Sesame oil and White Pepper to a jug. Add the remaining garlic and ginger and stir to combine.
Heat two medium sized frying pans over a medium-high heat. Add a drizzle of sunflower oil and the marinated chicken to the first pan..
Stir fry the chicken over a high heat for 4-5 minutes until nicely browned, adding the green beans in for the last couple of minutes
Pour the sauce into the second pan and allow to bubble until thickened (around 2-3 minutes)
Add the sauce and the water chestnuts to the pan of chicken and green beans. Stir to cook for a couple of minutes more until combined, sticky and the chicken is cooked through.
Put the Korean Chicken Stir Fry on to serving plates and sprinkle with sesame seeds and the spring onions. Serve with with rice or noodles,