Heat the oil in a saucepan, add the garlic, ginger and green chilli and saute over a medium heat until the garlic begins to colour. Add the cumin and saute for a minute or two, then add the onions. Cook until the onions are soft, then stir in the turmeric and chilli powder. Increase the heat to high and add the tomatoes. saute for 2-3 minutes until the tomato juices begin to dry up, being careful the mixture does not stick. Lower the heat to medium once again and gently stir in the cheese. Cook until well heated through. Add salt to taste, then stir in the fresh coriander. Remove from the heat, sprinkle with the chaat masala and serve.