Prepare the Piri Piri Sauce as given in this link. https://mareenasrecipecollections.com/piri-piri-sauceperi-peri-sauce-recipe/
Place the chicken pieces in between plastic wraps. Flatten them evenly using a rolling pin or mallet.
Score either sides of the chicken pieces, with a knife. You can omit this step as this is optional.
Apply piri piri sauce all over the chicken pieces.
Refrigerate for at least an hour. (I would strongly recommend marinating the chicken overnight or 7-8 hours so that the chicken absorbs all the flavours.)
Heat a grill pan.
Apply a light coat of oil on the pan.
Carefully place the chicken pieces on it and cook on high flame.
When the bottom portion turns slightly brown, flip the pieces. When they start to brown, reduce the heat to low, cover and cook till it turns a shade darker. Flip and continue till the chicken is done. You can check the doneness by inserting a knife to the thickest part of the chicken. If the juices run clear, the chicken is done.
Serve hot with accompaniments of your choice.