In a pressure cooker add in the Moong dal along with Onion, tomato and the required water .Cook for about 4 whistles in Medium flame or till it is done.
Once the pressure is completely released open the cooker and mash it well.
Add in Sambar powder, Chilli powder, Turmeric powder and salt add little water if it is too thick and mix well .Heat a pan with oil. To this add Mustard Seeds, Cumin seeds and hing.
Next add in Dry Red Chili and Curry Leaves .Let tit splutter and then add in the Dal mixture. Give a good mix and check for salt and spice add it anything is less. Let it cook for 5 mins in a medium flame. When it starts boiling switch off the flame and garnish with coriander leaves.