Chop up the mango pickle to break up any large pieces of mango.

Cut a slit down the middle of the green chilies, and cut the chilies into 2-inch pieces.

Chop the chicken thighs into 2-inch pieces. In a medium bowl, combine chicken, half the mango pickle, yogurt, and some salt. Stir to coat and set aside while you prepare the remaining ingredients, about 15 minutes.

Using a spice grinder or mortar and pestle, coarsely grind fenugreek, mustard, fennel, nigella, and cumin seeds.

Set Instant Pot to saute mode. Add the oil and allow it to heat up. Add onions and cook until onions are softened and translucent.

Add the coarsely ground spice mixture. Add turmeric powder. Let the spices toast with the onions for 30-45 seconds. It will start to smell very fragrant and the spices will start to turn golden.

Add the ginger-garlic paste. Cook that for about a minute. The ginger and garlic will start to turn golden and the raw smell will dissipate. Stir and scrape the bottom to keep the paste from sticking and burning.

Add the tomatoes and deglaze the pan by scraping up anything that sticks. Cook until the tomatoes are jammy and the tomatoes no longer hold their shape.

Add the red chili powder and allow it to bloom for about 10 seconds.

Add the chicken and all of the marinade. Add salt and 1/2 cup of water. Stir well and deglaze anything that has stuck to the pan.

Cook under high pressure for 4 minutes. Followed by a quick release.

Set the Instant Pot back to saute mode. Add the remaining pickle and green chilies. Mix well. Cook for 3-5 minutes until the sauce thickens to desired consistency.