Prepare all ingredients by washing and slicing the carrots and celery, dicing the onion, and mincing the garlic.
In a large pot, heat the olive oil over medium heat. Add the Italian sausage and cook for 5-7 minutes, breaking it apart as it browns.
Add the diced onion, minced garlic, sliced carrots, and diced celery to the pot. Sauté for about 5 minutes until tender.
Stir in the dried thyme, oregano, and red pepper flakes. Cook for another minute, then pour in the chicken broth and diced tomatoes. Bring to a boil, then reduce heat and simmer for 10 minutes.
Add the cheese tortellini and cook according to package instructions, usually about 3-5 minutes.
Stir in the fresh spinach and cook until wilted, about 1-2 minutes. Season with salt and pepper to taste, then serve topped with grated Parmesan cheese.