Heat up a wok and add the oil. When the oil is heated, add the garlic, onion, dried red chilies and stir-fry until fragrant or when you smell the spicy aroma of the chilies. Add the cashew nuts and follow with the chicken. Stir-fry the chicken until the surface turns opaque. Add all the ingredients for the Sauce into the wok and continue to stir-fry until the chicken is cooked. Stir-in the scallion, dish out and serve immediately with steamed rice.