Dry roast the coriander seeds and black peppercorns in a small pan until they become aromatic. Remove from the heat and grind to a powder. Combine with the turmeric and set aside.
Heat the oil in a large wok and fry the mustard seeds until they start to pop. Add the onion, ginger, garlic and curry leaves and fry until the onions become translucent.
Add the chicken and fry until golden brown, then add the coriander, pepper and turmeric spice mix and fry for a further minute, stirring constantly.
Add the vinegar ans 125 ml water. Simmer for 2 minutes then add the coconut milk, the mango cubes and salt to taste. Gently simmer for a further 5 minutes, being careful not to allow the coconut milk to boil.