Heat the olive oil in a large soup pot or Dutch oven over medium-high heat. Add the diced chicken, 1 teaspoon of Italian seasoning, and season with salt and pepper. Cook for 4 to 5 minutes, stirring occasionally, until the chicken is browned on all sides.

Add the onions, carrots, celery, sun-dried tomatoes, and minced garlic to the pot. Cook for 3 to 4 minutes, stirring frequently, until the vegetables become translucent.

Sprinkle the flour gradually over the vegetables while stirring constantly to coat everything and prevent clumping. Once incorporated, add the tomato paste if using and stir well. Cook for about 1 minute.

Gradually whisk in the chicken broth, stirring constantly to prevent lumps. Scrape the bottom of the pot to deglaze. Bring the mixture to a rolling boil.

Add the pasta, remaining 1 teaspoon of Italian seasoning, salt, and pepper to taste. Cover the pot with a lid, reduce heat to low, and simmer for 15 to 20 minutes. Check pasta after 15 minutes. The chicken should reach 165°F internal temperature and pasta should be al dente.

Remove the lid and reduce heat to medium-low. Stir in the heavy cream, fresh spinach, and grated Parmesan cheese. Simmer uncovered for 5 minutes. Add extra broth if soup is too thick. Taste and adjust seasoning as needed.