If the prawns are large, cut each in half lengthways, otherwise leave them whole. Mix the black bean paste, oyster sauce, vinegar, white pepper powder in half a cup of chicken stock and set aside.
Heat the remaining chicken stock in a wok or a pan, bring it to a boil. Dust the chicken and prawns in half tablespoon of cornflour and gently slide them into the boiling stock.
Mix the remaining cornflour in half a cup of water. Lower the heat and simmer for about three minutes. Add the blended sauces, cornflour mixture and salt and simmer for half a minute.
Drizzle chilli oil and serve hot, garnished with spring onion greens.