In a large pot, heat olive oil over medium heat. Add the Italian sausage and cook, breaking it apart with a wooden spoon, until browned.
Add the chopped onion and minced garlic to the pot. Sauté until the onion is translucent.
Stir in the sliced zucchini and cook for an additional 3 minutes.
Add the diced tomatoes, chicken broth, dried basil, dried oregano, salt, and pepper. Bring to a boil, then reduce the heat and let it simmer for 20 minutes.
Stir in the spinach leaves and cook until wilted. Adjust seasoning if needed.
Serve the soup hot, topped with grated Parmesan cheese.
Notes
Feel free to use turkey sausage for a lighter version. Can also add a pinch of red pepper flakes if you prefer a bit of heat.