Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chicken pieces and cook until lightly browned on all sides, about 5 minutes. You do not need to cook them completely through yet.
Add the chopped onion, carrots, and celery to the pot. Cook until the vegetables begin to soften, about 5 to 7 minutes.
Stir in the minced garlic, Italian seasoning, salt, and pepper. Cook for 1 minute until fragrant.
Pour in the chicken broth and add the diced tomatoes (with their juice). Bring the mixture to a simmer. Reduce the heat to low, cover, and cook for 10 minutes, or until the chicken is cooked through.
Remove the chicken from the pot and shred it using two forks. Return the shredded chicken to the pot.
Stir in the heavy cream and increase the heat slightly to maintain a gentle simmer. Do not allow the soup to boil after adding the cream.
Add the refrigerated tortellini to the soup. Cook according to package directions, usually 3 to 5 minutes, until the pasta is tender.
Remove the pot from the heat. Stir in the grated Parmesan cheese until it melts into the broth, making it creamy.
Stir in the fresh spinach until it wilts into the soup. Taste and adjust salt and pepper if needed.
Serve immediately for a hearty winter meal.
Notes
For a thicker, velvety texture, you can whisk 2 tablespoons of all-purpose flour with 2 tablespoons of butter to create a roux before adding the broth.
If you prefer a Tuscan Chicken Soup flavor, add 1/2 cup sun-dried tomatoes (drained) along with the broth.