Crumble sausage in a Dutch oven, add onion.
Cook over medium high heat until meat is no longer pink.
Add garlic and cook one minute.
Stir in diced tomatoes, chicken broth, and water.
Bring to a boil.
Add in tortellini and return to a boil.
Cook 7-9 minutes or until tortellini is tender, stir occasionally.
Reduce heat.
Add spinach, basil, pepper, and pepper flakes.
Cook 2-3 minutes until spinach is wilted.
Serve hot with cheese if desired.