Saute veggies. Heat a stockpot over medium-high heat. Add the olive oil, onions, and cook until softened, about 3-4 minutes. Add garlic and seasonings (salt, pepper, red pepper flakes, and Italian Seasoning) and stir for another minute.
Add liquids. Add chicken broth, crushed tomatoes, whole milk, and tomato paste. Bring mixture to a boil, reduce heat, add parmesan rind (if using) and rotisserie chicken. Cook for about 10-15 minutes.
Add the tortellini and spinach. Cook tortellini until softened, about 4-5 minutes. Add spinach and stir until wilted.
Serve soup. Serve with a dollop of ricotta cheese, freshly shaved parmesan cheese, and crusty bread.
Notes
For added convenience, use rotisserie chicken for quick preparation.