Marinate chicken pieces ( smaller pieces) in black pepper and oyster sauce for 1 hour.
Cut the capsicum, onion, ginger and garlic into fine slices.
Fry the onion and when half cooked, add in capsicum, garlic and ginger.
When the onion becomes golden brown, add the marinated chicken.
Add black pepper and salt (less than the normal taste, since you would add soya sauce later).
Cover and cook for 15 mins.
Add soya sauce and vinegar and again cook for another 10 mins.
Garnish with chopped spring onions.