Prepare all of your ingredients so that they are ready to go into the instant pot when it’s time.
Make the meatballs: In a medium-sized bowl, combine the ground chicken, egg, breadcrumbs, parmesan cheese, 1 tablespoon parsley, salt, pepper, and 2 minced garlic cloves. Scoop, separate, and roll the mixture into 1 to 2 tbsp-sized meatballs. (I had about 26 meatballs. You might have a bit more or less depending on their size.)
Set your instant pot or pressure cooker to the “sauté” setting. (See notes if you don't have a "sauté setting.) Allow it to heat up for about a minute, then add in 2 tablespoon of olive oil. Carefully swirl the oil around so it coats the bottom of the pot.
Add the meatballs to the pot. Try not to overcrowd them. You can cook them in batches if you need to. Allow the meatballs to cook for about 3 minutes without touching them. After 3 minutes, try lifting them from the pot. If they are stuck, let them cook for another minute or two. The meatballs will release from the pot once they are perfectly golden brown.
Flip the meatballs over and allow them to brown the same way on the other side. When done, remove them from the pot and place them on a clean plate.
With your pot still on the sauté setting, add in the other 2 tablespoon of olive oil, onion, carrots, celery, other 2 minced garlic cloves, and 2 tablespoon parsley. Use the vegetables to scrape the chicken scraps from the bottom of the pot. (If you don’t scrape the pot properly, it will stop mid-cooking and give you a burn warning!) Stir and cook until the carrots soften a bit and the onions start to become translucent.
Turn off the sauté setting. Add back in the meatballs, along with the chicken broth, oregano, basil, acini di pepe, salt, and pepper. Gently give everything a stir, being careful not to break apart the meatballs.
Cover the pot with the lid and set the valve to “seal.” Pressure cook on high for 3 minutes. Allow the pot to naturally release for 15 minutes before flipping the valve to “vent” and manually releasing any remaining pressure.
Remove the lid and gently stir in the spinach until it wilts.
Serve soup hot with a sprinkle of parmesan cheese on top and a side of your favorite crusty bread!