Set the Instant Pot to the 'Sauté' function and heat the olive oil.
Add the chopped onion and sauté for about 3-4 minutes until translucent.
Stir in the minced garlic, diced carrots, and diced celery. Sauté for an additional 3 minutes.
Season the chicken breasts with salt and pepper, then nestle them into the vegetable mixture.
Pour in the chicken broth, diced tomatoes, and Italian seasoning. Stir to combine.
Close the lid of the Instant Pot and set the valve to sealing. Cook on 'Manual' high pressure for 8 minutes.
Once cooking time is complete, perform a quick release of the pressure by carefully turning the valve to venting.
Remove the chicken breasts, shred them with two forks, and return the shredded chicken to the pot.
Add the tortellini and fresh spinach to the soup. Stir well and set the Instant Pot to 'Sauté' again for about 5 minutes, until the tortellini is cooked through and the spinach is wilted.
Taste and adjust seasoning if necessary. Serve hot, garnished with grated Parmesan cheese and fresh parsley, if using.
Notes
Feel free to add more vegetables or adjust seasoning to taste.