Heat a 5 quart stock pot or Dutch oven to medium-low and add olive oil. 2. Add celery, carrot, and onion, and season with salt and pepper to taste. Cook 5-6 minutes, stirring occasionally, until lightly softened. 3. Add garlic, Italian seasoning and red pepper flakes, and stir well. Cook 1 minute, until fragrant. 4. Add chicken stock, red wine vinegar, and tomatoes. Bring to a boil. Reduce heat to low, Cover and simmer for 30 minutes. 5. Add cooked chicken and tortellini, and simmer 5 minutes more, until tortellini is cooked through. Serve with plenty of grated parmesan cheese.