Turn Instant Pot to Sauté and heat 1 tablespoon oil in pot. Add onions and cook until softened, about 3-4 minutes.
Add garlic, carrots, and celery, and sauté for 1-2 more minutes, or until garlic is fragrant and celery is beginning to soften.
Place whole chicken on top of vegetables, then pour in water, bay leaves, peppercorns, salt, and freshly cracked black pepper.
Secure lid and set to Manual High Pressure for 20 minutes.
When timer is up, Quick Release lid carefully. Carefully transfer whole chicken to a large cutting board, keeping an eye open for any liquid from the cavity. It will be very hot!
Turn Instant Pot on Sauté mode. Add pasta.
While pasta cooks, with two forks, shred chicken off the bone. When pasta is tender, return chicken pieces to soup, discarding bones. Stir in fresh parsley and fresh lemon juice.
Add more salt or pepper to taste.
Portion into bowls and serve hot.