Preheat the Instant Pot by selecting the Sauté setting. Heat the oil in the preheated pot for a few seconds, then add the mustard seeds and leave for about 30 seconds, or until they start to splutter. Add the onion, ginger, garlic, chile, and a pinch of salt and cook until the onion is translucent, about 2 minutes. Stir in the turmeric, garam masala, and black pepper and cook for 30 seconds. Add the tomato and 1/4 cup (60 ml) of the water and cook, stirring occasionally to prevent sticking, until the tomato is softened, about 2 minutes. Add the butternut squash, coconut milk, remaining 3/4 teaspoon of salt, and remaining 1/2 cup (120 ml) of water. Add the lentils to the pot, and give it a good stir to combine and scrape up any bits of tomato from the bottom of the pot. Select the Cancel setting.