Pressure cook dal along with salt, turmeric, ginger and slit green chillies until soft. Whisk it to make a smooth paste.
Transfer to a pot. Add diced tomatoes and cook till tomatoes are soft. (You can add the tomatoes in the pressure cooker, but I prefer to use it after the dal is cooked. It helps to retain the yellow colour of dal and the Tomatoes will not become mushy).
Add chopped cilantro and continue to cook for 5 minutes. Switch off the flame.
Heat oil in a small pan. Add mustard seeds. When they splutter, add cumin seeds, asafetida, curry leaves and cut red chillies. Saute for few seconds. Pour this tempering over the dal. Cover the pan immediately.
Serve along with steamed rice or roti garnished with some more chopped coriander.