Heat olive oil in a large soup pot over medium-high heat. Add diced chicken, 1 teaspoon Italian seasoning, salt, and pepper. Cook for 4–5 minutes until browned on all sides. Remove and set aside.
In the same pot, add onions, carrots, celery, sun-dried tomatoes, and garlic. Cook for 3–4 minutes until softened and fragrant.
Sprinkle flour over the vegetables and stir to combine. Add tomato paste if using and mix well.
Slowly whisk in chicken broth while scraping the bottom of the pot to release browned bits. Stir until smooth.
Bring the soup to a gentle boil. Add pasta and the remaining teaspoon of Italian seasoning. Reduce heat, cover, and simmer for 20 minutes or until pasta and chicken are cooked through.
Stir in heavy cream, spinach, and Parmesan cheese. Simmer for an additional 5 minutes until the soup thickens slightly and spinach wilts.
Taste and adjust seasoning if needed. Serve warm with extra Parmesan and cracked black pepper.
