Season the chicken thighs with salt and pepper on both sides. Let them sit while you prep the onion and garlic.
Set the Instant Pot to the sauté function and heat the olive oil. Add the chicken thighs, skin-side down, and sear until the skin is golden and crisp, about 4 minutes per side. Remove the chicken and set aside.
In the same pot, add the sliced onion and a pinch of salt. Sauté until the onion is soft and translucent, about 3 minutes. Add the minced garlic and cook for 30 seconds until fragrant.
Pour in the chicken broth, lemon juice, and lemon zest. Stir to loosen any browned bits from the bottom of the pot.
Return the chicken to the pot, skin-side up. Sprinkle oregano and thyme over the top. Lock the lid in place and set the Instant Pot to high pressure for 8 minutes.
When the timer ends, allow a natural release for 5 minutes, then quick-release any remaining pressure. Open the lid carefully.
If you’d like a thicker sauce, switch to sauté and simmer for a few minutes, or stir in the butter until melted and glossy. Taste and adjust salt if needed.
Serve the chicken with the lemony sauce spooned over the top. Garnish with chopped parsley if you like a fresh green finish.