First, add the oil to a large frying pan and heat to a medium heat. Add in the mustard seeds. When they start to pop, add in the cumin seeds, coriander, turmeric, curry leaves and chilli flakes.
Stir for a few seconds, then add the onion. Fry for approx 8-10 minutes on a low to medium heat until soft and browning.
Add in the garlic, ginger and the remaining squash and stir for another 3-4 minutes,
Now add the lentils, tomatoes and water. Stir well, then turn down the heat and put the lid on the pan.
Simmer for 30 minutes, stirring occasionally. Add more water if needed. The squash should be soft.
Stir in the coconut yogurt.
Season well.