Marinate the chicken legs with the above seasoning for a few hours, or preferably overnight in the refrigerator. Take them out at least an hour before cooking.
Heat up a grill pan with a little bit of oil and once the pan is red hot, add in the chicken pieces, reduce the heat to maintain the temperature, and let the chicken cook for a few minutes.
Leave any marinade in the bowl for later use. Once the edges of the meat start to brown, then flip over to the other side and grill for a further few minutes.
Dish up onto serving plates. In another pan, heat up some oil and toss in the onion slices and capsicums, stir-fry and dish out.
In the same pan, put in the chicken marinade, add in the ground black pepper, oyster sauce and water, let it simmer.
Fine tune to taste and add in the thickening. Arrange the onions and capsicums onto the serving plates with the chicken pieces and pour over the sauce.
Serve immediately and enjoy.