Slice the chicken into strips around 5-6mm (¼") wide and 3-4cm (1½-1¾") long.
Mix all of the ingredients for the marinade together and add them to the chicken, and allow to marinate whilst you prepare the remaining ingredients.
Slice the garlic as thinly as you can.
Peel and cut the ginger into batons approximately 2-3mm (⅛") in profile.
Slice the spring onion as finely as you can.
Place all of the ingredients for the sauce into a bowl and mix well.
Add 3-4cm (1½-1¾") of oil to a large wok and heat it to 180° C or 350°F.Fry your chicken, in batches if required, for 3-4 minutes until crispy and cooked through, then transfer to some kitchen paper to drain any excess oil.
Carefully drain the wok of oil, other than a scant coating, and return it to a high heat. If you are worried about draining the wok, you can do this in a separate frying pan, use something around 28cm or 11" in diameter and nonstick if possible.
Throw in the chillis, garlic, and ginger and stir fry for 30-40 seconds.
Pour in the sauce; it will thicken after 30-60 seconds.
Add the chicken, toss to coat and serve sprinkled with the spring onions.