Heat the oil in a deep pan. Add the mustard seeds. When they splutter add the ginger, garlic and onions and sauté till golden. Add the curry leaves, turmeric powder, red chilli powder, coriander powder, crushed black peppercorns and sauté for a minute.
Add the tomatoes and salt to taste and sauté till the tomatoes are soft. Stir in the chicken pieces, cover and simmer till the chicken is cooked and the mixture is almost dry. Stir the dish occasionally. You can sprinkle little water if needed in order to prevent scorching.