Pound the garlic and ginger to a fine paste in a pestle and mortar, then set aside.
Heat the oil in a large frying pan then add the onions, curry leaves and green chilli. Cook over a medium heat until the onions are brown.
Add the garlic/ ginger paste and cook for 5 minutes, stirring occasionally . Add the coriander and turmeric plus a good pinch of salt. Mix well and cook for a further 5 minutes.
Add the chicken to the pan and stir through, then add 225 ml water and the garam masala, Mix well, then cover and cook over a low heat for 5 minutes, or until the chicken is cooked through.
Stir in the ground pepper, then remove from the heat and serve.