Wash the dal under running water and then in a pressure cooker or a heavy bottomed saucepan, boil the dal with the turmeric powder, salt, sugar and chopped green tomatoes.
In case you are using a pressure cooker, then do not add too much water, just enough for the dal to boil, perhaps only one whistle.
When the dal is ready for tempering, in a small tadka pan, heat 1/2 tbsp of mustard oil and add the mustard seeds and dry red chillies. Toss them around till the mustard seeds splutter and start giving out a nice aroma.
Then pout the tadka over the dal and tunr on the heat to cook the dal for a couple of minutes more. Adjust the seasoning and add more water if required. The tomatoes are more or less quite a pulp in the dal.
Finally garnish with coriander leaves and drizzle mustard oil over top and switch off the flame. The taste of raw mustard oil with the dal is phenomenal.
Serve it with some steamed rice.