Chop up the chicken into little bite size portions, place in a bowl, and add all the marinade ingredients in. Mix thoroughly, and leave aside while you get the other ingredients ready.
Chop up the garlic fairly finely.
Slice the capsicums (bell peppers) up into roughly 2.5cm (1") squares.
Slice the spring onions (scallions) into 5cm (2") lengths.
Sauce
Mix all the sauce ingredients in a medium bowl and set aside.
Cooking the sweet and sour chicken
Heat 1 Tbsp of the sesame oil in a large wok on high heat, and when almost smoking, brown the chicken pieces for about 2 minutes, turning and flipping. We are not cooking the chicken, just adding a touch of colour and flavour, so lightly browned is what we are after. Tip out onto a plate.
Heat the second Tbsp of oil in the same wok, still on high heat, it'll only take a few seconds. Then fry the garlic, peppers and spring onions (scallions) for 30 seconds.
Add the sauce, stir and bring to a boil.
When the sauce is bubbling at the edges, add the chicken, stir, and bring back to a boil. Then lower the heat down and simmer for 5 minutes or until the chicken is cooked through. As we are using small chicken breast portions, 5 minutes should be enough. That's it, serve hot.