1) Heat the oil in a large pan, add the curry leaves and mustard seeds and mix well.
2) Add the tomatoes and cook for 5 minutes, stirring, then add the ground coriander, chili powder, cumin, salt and garlic and continue to cook for a further 2-3 minutes.
3) Raise the heat then add the cubed chicken and stir fry for 5 minutes.
4) Pour in the water, bring to the boil, then simmer for 20-30 minutes, stirring from time to time, until the chicken is cooked and the sauce has thickened.
5) To serve - transfer to a heated serving dish and sprinkle the sesame seeds and chopped coriander over the top. Serve immediately.