Press the saute button on the Instant Pot. When it displays hot, add the oil and then add the cumin seeds and mustard seeds. Let them pop.
Then add the onion, garlic, ginger and green chili. Saute 2 to 3 minutes.
Add the chopped tomatoes, stir and deglaze the pot. There shouldn't be any browned bits stuck to the bottom of the pot. Add the coriander powder, red chili powder, garam masala, smoked paprika, salt and sugar. Mix until combined.
Add the butternut squash and water (1/3 to 1/2 cup, squash releases a lot of water when pressure cooked).
Close the pot with its lid. Press the manual or pressure cook button and cook on high pressure for 8 minutes. Let the pressure release naturally for 5 minutes and then do a quick release.
Open the pot, press saute and then mash the cooked squash with a potato masher. You may also use a fork.
Cover the pot with a glass lid and let it simmer on saute mode for 7 to 10 minutes until the excess water evaporates and bharta becomes little dry. Note: it splutters, so best to cover the pot with a glass lid when it's simmering on saute.
The bharta will thicken more as it cools down. Add cilantro.Garnish with more cilantro and serve butternut squash bharta with roti, paratha or rice.
To make this using the oven and stove-top, pre-heat oven to 425 F degrees. Drizzle the squash cubes with oil and roast at 425 F for 25 to 30 minutes or until very soft. Remove from oven.
Heat oil in a pot on medium heat. Once the oil is hot, add the cumin seeds and mustard seeds. Let them pop and then add the onion, garlic, ginger and green chili. Saute for 2 to 3 minutes until onions soften. Then add the tomatoes and cook for 4 to 5 minutes. Add the spices, salt and sugar and stir for 30 seconds.
Add the roasted squash and mash with a potato masher. Do not add any water. Stir and let it simmer for 5 minutes on medium-low heat, stirring often. Garnish with cilantro and serve.
This bharta is not very spicy. If you prefer spicy food, add more green chilies and more of the red chili powder.