Cook the Chicken: Heat olive oil and butter in a large pot over medium heat. Add cubed chicken, season with salt and pepper, and cook until lightly browned on all sides (about 5 minutes). Remove the chicken from the pot and set aside.
Sauté Aromatic: In the same pot, add the diced onion and cook for about 3 minutes, until softened. Stir in the minced garlic and red pepper flakes, cooking for 1 minute until fragrant.
Build the Broth: Pour in the chicken broth, scraping up any browned bits from the bottom of the pot for extra flavor. Stir in the heavy cream, sun-dried tomatoes, and Parmesan cheese. Let the soup simmer gently for 10 minutes, stirring occasionally.
Add Chicken and Seasonings: Return the cooked chicken to the pot and add the Italian seasoning. Simmer for another 10 minutes, ensuring the chicken is fully cooked and the flavors meld together.
Finish with Spinac: Stir in the baby spinach and cook for 2 minutes, just until wilted. Taste and adjust seasoning with more salt and black pepper, if needed.
Serve and Enjoy: Garnish with fresh parsley or basil. Serve hot with crusty bread, over rice, or with a side salad for a complete meal.