Combine the cornstarch, vinegar and 1 tablespoon of soy sauce in a bowl and mix to combine.
Stir in the chicken and let marinade for 30-60 minutes.
While the chicken is marinating, combine the remaining soy sauce, coconut sugar, chicken stock and five spice in a bowl and stir to combine. Set aside.
Heat a wok on high heat until it starts to smoke.
Add the oil, let it heat for 10 seconds, then add half the chicken.
Stir fry for about 2-3 minutes, until chicken is browned and a crust has formed on the outside.
Remove with a slotted spoon and set aside. Add additional oil to the wok if needed (there should be at least 1 tablespoon of oil remaining).
Add the remaining chicken and stir fry in the same manner as the first. Remove and set aside.
Turn the heat down to medium and add the garlic and ginger. Stir fry for about 30 seconds.
Add the green onions (reserving the 2 tablespoons of chopped green onions for garnish) and cook for about 30 seconds.
Turn the heat back to high and add the chicken and the sauce to the wok.
Cook for about 2 minutes, or until the sauce has thickened and coated the chicken.
Remove from heat and serve garnished with green onions, sesame seeds (optional) and white rice, fried rice.