Heat some oil in a large wok or frying pan over high heat.
Cook the chicken in batches until they are lightly golden all over. They do not need to be cooked all the way through because you will cook them some more later.
Use a slotted spoon to remove the chicken to a large plate.
Add the garlic and onion to the pan, and cook for about 1 minute until the garlic starts to release its aroma.
Add the remaining vegetables to the pan, and toss everything together.
Cook for several minutes until the vegetables start to soften slightly. I like my vegetables to retain some crispness, so I only cook them for several minutes.
Return the chicken to the pan, together with any juices which have collected on the plate.
Pour the Black Pepper Sauce into the pan.
Give everything a good stir and let the sauce simmer gently for a few minutes until it has thickened nicely, and the chicken has warmed through.
Taste the sauce for seasoning. If the sauce is too thick or strongly flavoured, add a dash of hot water.
Garnish with red chillies and coriander (cilantro) before serving.