In a large pot over medium heat, add the diced onion and minced garlic. Sauté until the onion is translucent.

Next, add the sausage to the pot, cooking until browned. Use a spatula to crumble the sausage as it cooks for even texture.

Once the sausage is browned, pour in the chicken broth and add the diced tomatoes along with their juice. Stir well to combine everything.

Sprinkle in the Italian seasoning, salt, and pepper. Bring the mixture to a gentle boil, allowing the flavors to meld together.

Reduce the heat slightly, and add the tortellini to the pot. Let it simmer according to the package instructions, usually about 3-5 minutes, or until they float to the top.

Finally, stir in the chopped spinach and cook for an additional minute until wilted. Adjust seasoning if necessary.

Ladle the soup into bowls, and top with grated Parmesan cheese if desired. Enjoy every warm, comforting bite!