In a medium pot, combine the rinsed red lentils, water, and turmeric powder.
Bring to a boil over medium heat, then reduce the heat and simmer for about 15-20 minutes, or until the lentils are soft and cooked through. If needed, add more water to keep the lentils from drying out.
Once cooked, lightly mash some of the lentils with the back of a spoon to create a creamy texture.
In a large pan, heat the vegetable oil over medium heat.
Add the mustard seeds, cumin seeds, and fenugreek seeds. Allow them to sizzle and pop for about 30 seconds.
Add the finely chopped onion, minced garlic, grated ginger, and slit green chilies. Sauté until the onion becomes golden brown and fragrant.
Stir in the chopped tomato, ground coriander, ground cumin, and chili powder (if using). Cook for about 5 minutes until the tomato softens and the spices are well combined.
Add the cooked lentils to the pan with the tempered spices and tomato mixture. Stir well to combine.
Pour in the coconut milk and bring the mixture to a gentle simmer. Cook for another 5-10 minutes, allowing the flavors to meld together.
Season with salt to taste.
Garnish the parippu with fresh chopped cilantro.
Enjoy your meal!