Heat 1 tbsp of cooking oil in a pot.
Remove the chicken from the marinade and place into the pot.
Sear chicken pieces on both sides, for 1 minute each. Don’t cook chicken all the way through. Reserve the marinade.
Remove chicken from the pot and set aside onto a plate or in a bowl.
Heat the remaining oil (1 tbsp) in the same pot.
Add onions and garlic. Saute for 1-2 minutes until fragrant.
Place the chicken back into the pot and add the reserved marinade.
Add water, brown sugar and whole peppercorns.
Turn the heat up to high, cover the pot and bring to a boil. Boil for 2 minutes.
Turn the heat down and simmer covered for 20 minutes or until the chicken becomes tender.
Add vinegar.
Stir and continue to cook for 5 minutes.
Turn the heat off.
Serve hot with steamed rice.