Set the instant pot to sauté mode and add the olive oil. Season the chicken with salt and pepper. Add in the chicken and sear to brown on both sides. Remove from the pot.
Add in the onion and cook for about 8 minutes, scraping the pan to get any of the brown chicken flavor from the bottom. Cook until the onions are starting to brown on the edges.
Add in the garlic and cook 2 minutes. Add in the lemon juice and scrape the bottom of the pan again. Add in the Italian seasoning and chicken stock and stir to combine.
Add the chicken back in the pot and cover. Set to pressure cook for 7 minutes and make sure the valve is set to seal. It will take a few minutes to come to pressure.
Once it is done, allow the pressure to naturally reduce for about 10 minutes, then switch the valve to release the remaining pressure. Serve.