1. In a large pot over high heat, combine the spinach and chicken broth. Heat to boiling, then reduce heat to low.
2. Saute onion and garlic and add to broth. Let simmer 10-15 minutes.
3. In a separate pot, cook tortellini till al dente. Cooking tortellini in broth will cause broth to get thick due to the starch and the tortellinis to get mushy.
4. Season with basil, salt, and pepper.
5. Add tortellini to broth at serve time and sprinkle parmesan cheese on top.