Wash the dals 2-3 times or till the water runs clear * see note#3. Soak in plenty of water for at least 45-60 mins (if you are using chana dal) or at least 20 mins if you are not using chana dal.
While the dal is soaking prep up the rest of the ingredients. When ready, heat oil in a pressure cooker and fry the minced green chillies, ginger and garlic and fry for a few seconds. Then add the onions and fry them until they turn light golden - do not brown them.
Add the chopped coriander and fry for a few seconds. Next, add the tomatoes, salt to taste and fry until the tomatoes turn mushy.
Add in the spice powders and fry on a reduced heat so as to not burn them.
Drain the soaked lentils and add them to the mixture and mix well. Now add 2-1/2 - 3 cups water and bring the mixture to a rolling boil. Check salt to taste and adjust accordingly
Once the water comes to a boil, place the lid and the weight (whistle) and cook on full heat till the cooker releases 1 whistle. Reduce the heat to a complete sim and cook for a further 12 mins.
Turn off the heat after 12 mins and let the pressure cooker cool down until you are able to release the weight easily.
Open, mix and adjust consistency/thickness of the dal by adding water little by little if you find it too thick. If you find it too thin then place it back on the heat and simmer (on a low heat) for 2-3 minutes. Also, at this stage you can add an additional chopped tomato or salt to adjust the tang/saltiness. You may also use a few drops of lime instead of tomato.
To prepare the tempering/seasoning heat the ghee in a small kadhai/pan and toss in the cumin and let them sizzle for a few seconds before adding the ginger, green chillies and onions. Fry until the onions turn pale/translucent. Pour this mixture over the prepared dal. Cover the lid immediately to trap the aroma of the tempering.
Garnish with chopped coriander and serve hot with chapathis or rice.