Gently heat oil in a wok or frying pan over medium heat. Add garlic, ginger and chilli powder. Cook and stir for a minute, then add chicken and increase heat to medium high. Continue to cook, stirring occasionally, till no longer pink in the centre.
Meanwhile, in a separate bowl mix the stock, soy sauce and cornflour. Once the chicken is cooked through add the liquid to the wok. Simmer for 3 to 4 minutes.
Add basil and simmer for a further minute (until basil is wilted).