Heat the oil in a large pan, add the curry leaves and mustard seeds and mix well.
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. Raise the heat then add the cubed chicken and stir fry for 5 minutes.
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.To serve - transfer to a heated serving dish and sprinkle the sesame seeds and chopped coriander over the top. Serve immediately.
Note: Yield: 4 Servings, Ready In: 30 Minutes, Degree of Difficulty: Medium