Combine all the marinade ingredients in a bowl and mix well.
Cut each chicken fillet into four pieces and tip into the bowl with the marinade. Cover and refrigerate overnight.
When ready to eat heat the oil in a wok, add the onions and stir fry until lightly browned then remove from the pan.
Add the chicken and its marinade to the wok and simmer, covered, stirring occasionally for about 15 minutes or until the chicken is tender and the mixture thick.