Heat the vegetable oil in a large dry pan to hot but not smoking.
Add the chicken in one layer in the bottom of the pan. Do this carefully so you don't splash the oil and get burnt.
Turn the heat down a little bit and let the chicken start to cook through. DO NOT STIR - this isn't a stir fry. You want the oil to crisp up the cornflour.
Make sure the cayenne pepper doesn't burn. When the chicken starts to cook through the bottom side (about 5 minutes), use a spatula and FLIP the chicken ONCE.
Distribute the uncooked chicken in one layer in the bottom of the pan. Cover with the onions and peppers.
Cover, turn heat down to medium and cook the chicken through (about 10 minutes).
Uncover. Turn heat backup to HIGH. Carefully, pour the sauce mixture all over the chicken. It will steam so be careful.
Stir the sauce through (stir constantly now) to ensure it doesn't stick. Cover all of the chicken and vegetables thoroughly.
Plate up over white rice.