Heat the olive oil in a large pot over medium heat. Add the onion, celery, garlic, leek, mushrooms, thyme, oregano, salt, pepper, and red pepper flakes. Cook for about 5 minutes, stirring occasionally.
Add the chicken broth to the pot and bring to a boil. Reduce the heat and simmer for about 10 minutes.
Add the chicken, sausage, and tortellini to the pot and simmer for about 15 minutes.
Serve the soup topped with Parmesan cheese.
Interesting Facts
This soup can be made in advance and reheated when ready to serve.
Leftover cooked chicken or sausage can be used instead of fresh.