In a large pot, heat a little oil over medium heat.
Remove the sausage from its casing and crumble it into the pot.
Cook the sausage until browned, about 5-7 minutes.
Add the chopped onion and garlic, sauté until translucent.
Stir in the carrots, celery, and bell pepper, cooking for another 5 minutes.
Pour in the diced tomatoes with their juice and chicken broth.
Add Italian seasoning, salt, and pepper, then bring to a boil.
Reduce the heat and let the soup simmer for 15 minutes.
Stir in the fresh spinach and cook until wilted.
Serve hot, topped with grated Parmesan.