Heat oil in a heavy bottomed saucepan. Fry turmeric, green chillis, ginger, garlic and onions till golden brown.
Drain the urad dal, and add the dal to the fry. Add salt and 1 cup water. Cook on low heat till dal is half cooked. Now add chopped tomatoes and garam masala. Add a little more water if dal is too thick. Cook till dal is completely cooked. Garnish with coriander leaves and serve.