Season the cubed chicken generously with salt, pepper, and half of the Italian seasoning. Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat.

Add the seasoned chicken to the pot and cook until lightly browned on all sides, about 5-7 minutes. Remove the chicken with a slotted spoon and set aside, leaving any rendered fat in the pot.

Reduce the heat to medium. Add the diced onion to the pot and sauté until softened and translucent, about 5 minutes. Add the minced garlic and chopped sun-dried tomatoes and cook for another 1 minute until fragrant.

Pour in 4 cups of chicken broth, scraping up any browned bits from the bottom of the pot. Bring the mixture to a simmer. Stir in the remaining Italian seasoning and red pepper flakes (if using).

Return the browned chicken to the pot. Let the soup simmer gently for 10-15 minutes, or until the chicken is cooked through and tender.

Reduce the heat to low. Stir in the heavy cream and the remaining 1 cup of chicken broth. Heat through gently; do not allow the soup to boil once the cream is added.

Remove the pot from the heat. Stir in the freshly grated Parmesan cheese until fully melted and the soup is creamy. Taste and adjust seasoning with salt and pepper as needed. Garnish with fresh parsley before serving hot.