Crumble sausage in a large soup pot; add onion. Cook and stir over medium heat until meat is no longer pink. Add garlic and cook 1 minute longer.
Stir in the broth (or water/bouillon), tomatoes, carrots, black pepper and pepper flakes. Bring to a boil and let cook 4-5 minutes or until carrots are tender.
Add tortellini and return to a boil. Cook for 4-6 minutes or until tortellini are almost tender, stirring occasionally.
Reduce heat; add spinach and basil. Cook 2-3 minutes longer or until spinach is wilted and tortellini are tender. Serve with grated Parmesan if desired.
