Wash and soak the dal in water for 10 minutes. While the dal is soaking, wash, peel and chop the vellari/yellow cucumber into cubes.
Take the ingredients given under 'To grind' and grind it to a fine paste in a mixer jar, using ¼ cup of water.
Heat a pressure cooker with oil given under 'tempering', splutter mustard seeds, cumin seeds, thrown in red chilies, hing and curry leaves.
Add the chopped tomatoes and saute for a minute, add the chopped vellari/indian cucumber and saute.
To this now add drained dal and chickpeas, Mix well. Add 3-4 cups of water, the vegetable should be covered with water, that is quantity we are looking for.
To this now add the ground paste, add ¼ cup water to the mixer jar, shake and add that water to the cooker. Add salt, mix well.
Close the lid of the pressure cooker, let it cook for 3-4 whistles. I sometimes allow 5 whistles too. Let the pressure fall on its own.
Once the pressure falls, open the cooker, be careful of the gust of steam. Mix well. Serve this delicious kootu with rice and a generous drizzle of ghee.
Any leftover kootu can be refrigerated for just a day. Since the kootu is made of dal and coconut, there is a high chance of it getting spoiled, if left outside for a long, especially in hot and humid climates.