Add the cilantro, garlic cloves, and walnuts to a small food processor. Process until very finely chopped for about 30-45 seconds.
Add a layer of chopped onions to Instant Pot. Layer the chicken thighs on top of the onion and sprinkle Khmeli Suneli evenly over the chicken. Pour the chicken broth over. Spread the walnut mixture over the chicken.
Close the lid of your Instant Pot and turn the valve to Sealing.
Press Manual or Pressure Cooker button (depending on your model) and use the arrows to select 10 minutes.
It should take about 12-13 minutes to come to pressure, depending on the temperature of the ingredients.
Once the Instant Pot beeps that the 10 minutes of cooking are done, do a natural pressure release for another 10 minutes. This means you let your Instant Pot release pressure naturally without touching it for 10 minutes.
After 10 minutes of natural pressure release, do a Quick Release. This will take about 2 minutes.
Carefully open the lid of Instant Pot and mix everything.
If the sauce is too thin, then remove the chicken to a plate, turn Instant Pot to sauté mode and cook for about 7-10 minutes, stirring occasionally. You may wish to add a tablespoon of flour at this point to thicken the sauce further. The sauce will thicken as it cools.Note: you don't have to remove the chicken, you can sauté the sauce with the chicken but it will mean that the chicken will continue cooking.