Wash and roughly dice the Chayote squash.
in the medium-sized pan, add chayote squash pieces, Cayenne pepper, ground turmeric, sliced Serrano pepper, salt, and a sufficient quantity of water, and bring the water to a boil over medium-high heat. Reduce the heat to medium/low, cover the pan with a lid and cook till squash pieces are soft.
Meanwhile, whisk the yogurt to ensure no lumps are present.
Using a food processor or dry grinding attachment of the mixer/grinder, grind the coconut and cumin seeds to a very smooth paste using as little water as possible.
Once the squash pieces are cooked, lower the heat and add the whisked yogurt and mix well.
Now add the ground coconut paste and bring to another boil.
Adjust the consistency and the seasoning if required.
Prepare the tempering on another stove. Heat oil in a small pan on medium heat and add mustard seeds. When they splutter, reduce the heat, add the curry leaves and whole red chillies. Add the seasoned oil along with the spices to the chayote squash curry and serve hot.