Brown the Sausage: In a large pot over medium heat, cook the Italian sausage until it is nicely browned. Drain any excess fat to keep your soup from being too greasy.
Sauté the Vegetables: Add the chopped onion and minced garlic to the pot. Sauté until the onion turns translucent and fragrant, about 3-5 minutes.
Add the Broth and Tomatoes: Pour in the chicken broth along with the canned diced tomatoes. Bring the mixture to a boil to meld those wonderful flavors together.
Introduce the Tortellini: Stir in the cheese tortellini along with the Italian seasoning. Let it cook according to the tortellini package instructions, usually about 3-5 minutes.
Finish with Spinach: Finally, fold in the fresh spinach until it wilts nicely into the soup. Season with salt and pepper to taste.
Serve and Enjoy: Ladle the hearty soup into bowls and sprinkle with grated Parmesan cheese for an extra touch of deliciousness. Enjoy while hot!