Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion, carrots, and celery. Cook until the vegetables soften, about 5 to 7 minutes.
Add the minced garlic to the pot and cook for 1 minute until fragrant.
Pour in the chicken broth. Stir in the Italian seasoning, thyme, and pepper. Bring the mixture to a simmer.
Add the shredded or diced chicken to the simmering broth. If using raw chicken breast, cook until done, about 10 minutes, then shred it directly in the pot. If using pre-cooked chicken, just let it heat through.
Add the refrigerated tortellini to the soup. Cook according to package directions, usually 3 to 5 minutes, until they float and are tender.
Reduce the heat to low. Stir in the heavy cream and grated Parmesan cheese until the cheese melts and the soup becomes creamy. Do not let the soup boil after adding the cream.
If using, stir in the fresh spinach until it wilts, about 1 minute.
Taste the soup and add salt as needed. Serve this hearty pasta soup immediately.
Notes
For the richest flavor, use high-quality chicken broth. This helps achieve that homemade restaurant style soup taste.
If you want a thicker soup, mix 1 tablespoon of cornstarch with 2 tablespoons of cold water to create a slurry, then stir it into the simmering soup before adding the cream.
Add a dollop of pesto when serving for an easy flavor variation, similar to a creamy chicken pesto tortellini soup.