In a large soup pot, melt the butter over medium-high heat. Add the chopped onion, minced garlic, and ground Italian sausage. Break up the sausage with a spoon as it cooks until it's browned and the onion is soft and clear.
Pour in the chicken bone broth and fire-roasted tomatoes. Stir in the cream cheese until it's fully melted and smooth, blending into the soup.
Add the chopped zucchini, dried basil, dried oregano, and black pepper. Bring the soup to a gentle boil, then reduce the heat to a simmer. Cook for about 15-20 minutes, or until the zucchini is tender.
Finally, stir in the baby spinach until it wilts, which should take about 3 minutes.
Ladle into bowls and garnish with a generous sprinkle of shredded Parmesan cheese before serving. Enjoy this wholesome and easy meal!