Season the chicken with salt and pepper. Layer the chicken, onion, potatoes, olives and Italian seasoning in a 6 quart Instant Pot®. Pour the soup and stock over the chicken and vegetables (the order is important, so don't stir until after the cooking is done).
Lock the lid and close the pressure release valve. Pressure cook on High pressure, setting the timer to 10 minutes (timer will begin counting down once pressure is reached- it takes about 15 minutes). When done, press Cancel and use the quick releasemethod to release the pressure.
Stir in the lemon juice. Season to taste. Sprinkle with crumbled feta cheese and chopped fresh parsley before serving, if desired.