Peel off the ashgourd, scoop out all the seeds and cube the kernel in to medium cubes. Measure 2 cups of pieces and keep aside.
Pressure cook the pigeon pea lentils with enough water till it turns soft. Keep aside once done.
Method
In a cooking pan add the ashgourd cubes, 1 cup of water, turmeric powder and cook in medium flame. The ashgourd cubes will turn soft and tender in 5-10 minutes.
Meanwhile take the grated coconut, tamarind, green chillies and cumin seeds in a blender/mixer and grind to fine puree. Include water as required for grinding.
Next include the ground coconut puree and cooked lentils to the cooked ashgourd cubes. Add salt and water if required. Bring it to boil and switch off.
Heat a tempering pan and add all the ingredients under "To temper" list. When the mustard seeds sizzle, pour it over the kootu. Ashgourd kootu is ready to serve with rice.
Notes
The ashgourd shouldn't cooked till mushy. Instead the cubes should be soft holding their shape.
You can use tamarind while grinding or use it's water to cook the ashgourd cubes. Either way it's same.
As green chilly is the only source of spice here, use it in bit more quantity. Otherwise kootu tastes bland.