Wash and Peel the ridge gourd or peerkangai and chop the peerkangai into thick chunks. Note - Retain the skin or peels to make chutney later.
Soak the Toor Dal in water for atleast 20 minutes.
Drain the water used for soaking lentils, add 1 cup water, turmeric powder and pressure cook the lentils until they are soft.
Once the lentils have cooked, mash it well and keep aside.
While the lentils are pressure cooking, heat a pan and add the chopped peerkangai with 1 cup of water and salt to taste. Cook this for about 5 to 7 minutes.
In a mixer grinder jar, add grated coconut, whole red chillies (break it for easy grinding) and cumin seeds (jeera). Grind this into a fine consistency paste by adding 1/2 cup water. Note - If using frozen coconut, use hot water for grinding. Now, add the cooked and mashed lentils to the peerkangai. Mix well.
Then add the coconut gravy paste. Mix well and add salt, if required. Let it reach one single boil and then switch off the flame.
Heat a small tempering pan, add oil, urad dal, mustard seeds, curry leaves and whole red chillies. Once the mustard crackles, pour the tempering over the kootu. Mix well and serve as side dish with chapati or rice.