1. Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened and translucent, about 5-7 minutes. Add the minced garlic and cook for another minute until fragrant, being careful not to burn it.

2. Add the cubed chicken breast to the pot with the onions and garlic. Cook, stirring occasionally, until the chicken is lightly browned on all sides and no longer pink.

3. Pour in the chicken broth and the can of diced tomatoes (undrained). Stir in the chopped celery, carrots, Italian seasoning, salt, and pepper. Bring the mixture to a gentle boil, then reduce the heat to low, cover, and let it simmer for 10-12 minutes, or until the vegetables are tender.

4. Stir in the fresh spinach. Allow it to wilt into the soup, which usually takes only 1-2 minutes. Once the spinach has softened, pour in the heavy cream and stir to combine.

5. Remove the pot from the heat and stir in the grated Parmesan cheese until it is fully melted and incorporated.

6. Taste the soup and adjust the seasonings if necessary. Serve hot and enjoy.