Heat the oil in a non stick frying pan over a medium-high heat. When hot, add the chicken and brown all over. Lift out with a slotted spoon and set aside.
Pour out all but 2 tbsp of the oil and reduce heat to medium. Add the chilli and stir and fry for a few seconds.
Return the chicken and its juices to the pan. Add 4 tbsps water and bring to a simmer. Reduce heat to low and cover. Simmer for 10 minutes.
Add the soy sauces to the pan together with the sugar and onions. Return to a simmer for 5 minutes or more, stirring from time to time, until the chicken is cooked through.
Serve with some plain rice and one or more vegetable dishes.