Add the curry leaves, mustard seeds to the pot where the chicken was - cooking for 30 seconds, then add the onions. Cook over a medium flame for 5 minutes then place a lid on the pan and cook over a low flame, until they turn soft and translucent. This should take about 20 mins, but be sure to stir occasionally. Once they are cooked, add the ginger and garlic paste, mixing to combine for 30 seconds before adding the tomatoes, to deglaze the sticky paste from the bottom of the pot.