Sift through the lentils and remove any pebbles. Soak the lentils in cold water for 15 minutes and then drain them.
Select the Sauté setting on the Instant Pot and let the pot heat up. Add 1 tablespoon of coconut oil or oil of choice, followed by the onion. Cook until the onion is translucent, 3 to 5 minutes.
Add the garlic, ginger, and serrano pepper, and cook for 1 to 2 minutes, stirring frequently to prevent sticking. Add the Ground Spices and stir to coat into the onions, and cook for about 30 seconds, stirring almost constantly.
Select the Cancel setting and pour in 2 3/4 cups water, using a wooden spoon to scrape up any browned bits on the bottom of the pot. Add the soaked and drained lentils, 1 teaspoon kosher salt, black pepper to taste, and tomatoes. Stir to combine.
Secure the lid and set the Pressure Release to Sealing. Select the Pressure Cook setting at high pressure and set the cook time to 10 minutes.
Once the 10-minute timer has completed, allow a natural pressure release for 10 minutes before manually releasing the steam.
While the dal is depressurizing, make the tadka. Heat a small frying pan or tempering pan over medium-high heat on the stove. Add the 1 1/2 - 2 tablespoons of the coconut oil and, once it’s hot and shimmering, add the mustard seeds. Once the mustard seeds start popping, add the cumin seeds for a few seconds. Finally, add the curry leaves and dried red chile peppers (if using). Keep stirring or shaking/swirling the pan to help cook the spices evenly and to prevent burning, for a total of 60-90 seconds, or until very aromatic and the curry leaves have shriveled, the chili peppers and cumin seeds have turned darker. Remove from the heat immediately to prevent overcooking.
Pour the tadka over the dal and stir to combine. If desired, garnish with additional fresh cilantro and taste for seasonings. Serve with white rice and other optional toppings, if desired.