In a large pot or Dutch oven over medium-high heat, cook the Italian sausage, breaking it up with a wooden spoon until browned, about 5-7 minutes.
Add the diced onion and cook for 3 minutes until softened. Stir in the garlic and cook for 30 seconds until fragrant.
Pour in the diced tomatoes (with juices), chicken broth, and Italian seasoning. Bring to a boil.
Add the pasta, stir well, and reduce heat to medium. Cover and cook for 12-15 minutes, stirring occasionally, until pasta is tender.
Stir in the fresh spinach and cook for 1-2 minutes until wilted.
Remove from heat and stir in Parmesan cheese. Season with salt and pepper to taste. Serve immediately with extra Parmesan if desired.