Season the chicken with 1 teaspoon kosher salt and set aside.
Add the butter to an Instant Pot and set to SAUTE. Once melted, add the onion, garlic, ginger, garam masala, chili powder, cumin, turmeric, and cayenne. Cook, stirring often, until the onion is soft and the spices are very fragrant, about 5 minutes.
Add the chicken pieces, stir to coat with the spices and onion, and cook, stirring often, just until the outsides start to brown, about 4 minutes. Add the tomato sauce and remaining 1/2 teaspoon salt. Stir to combine. Cover and cook on HIGH pressure for 8 minutes. Vent to immediately release the pressure.
Uncover and stir in the coconut milk. Turn the Instant Pot back to SAUTE. Bring the mixture to a simmer, stirring occasionally, and let it continue to simmer until the sauce thickens slightly, about 10 to 15 minutes. Turn the Instant Pot off, and then stir in the peas. Let cool for 3 to 4 minutes, and then stir in the Greek yogurt (do not stir in the Greek yogurt right away or it may curdle). Enjoy warm with rice or naan and a sprinkle of fresh cilantro.
Instant Pot Brown Rice: I’ve been playing around, and so far my favorite ratio is 1 cup long-grain brown rice to 1 1/4 cups water. Stir the two together, add a pinch of kosher salt, and cook on high pressure for 22 minutes. Let the pressure release naturally for 15 minutes. PERFECT. (Please note, this applies to long-grain brown rice only. Other rice types may have different cook times and liquid ratios.)
Store leftovers in an airtight container in the refrigerator for up to 5 days or freeze for up to 3 months. Let thaw overnight in the refrigerator. Reheat leftovers gently on the stovetop or in the microwave.