Add the lentils to a pressure cooker. You can pre soak the lentils for 30min to 1 hour for faster cooking/better digestion. You can alternatively also dry roast the lentils until aromatic and then continue from here.
Add the watermelon rind and turmeric powder. The amount of watermelon rind can be adjusted according to your taste.
Add enough water to cover the lentil rind mixture. You can always add more later to adjust the consistency.
Pressure cook for about 10 minutes. We cooked it for 5 whistles. This is one of those cases when "mushy" is totally a good thing :)
While that's cooking, place the coconut in a blender. The amount depends on your taste. You can avoid it if needed as well. It adds to the taste but can be skipped if health reasons don't permit it. I would recommend freshly grated coconut but I use frozen to good results as well.
Blend it into a paste with addition of little water if required. Set aside.
Open the cooker when done.
Add the coconut paste, pepper powder, gunpowder (idli chutney powder) and salt at this point.
Mix to combine. You can taste test to adjust seasoning according to your taste. If needed, add hot water to adjust the consistency. Adjust seasoning once again in that case.
In another skillet, add Ghee/ Oil of your choice. Add the ingredients given in the "Temper" section, starting with mustard seeds. Once it starts spluttering, add the lentils and asafoetida. Switch off the flame when the lentils turn reddish brown and then add the curry leaves. You can also add few cilantro leaves if you like.
Now add it to the Kootu/Dal. Combine.