In a large soup pot or Dutch oven, heat olive oil over medium-high heat. Add the sliced Italian sausage and cook until browned, about 5-7 minutes. Remove the sausage with a slotted spoon and set aside.

In the same pot, add diced onion, carrots, celery, and bell pepper. Sauté for about 5 minutes until the vegetables start to soften. Add minced garlic and cook for an additional 1-2 minutes.

Stir in tomato paste and cook for 1 minute to enhance its flavor. Add the diced tomatoes, Italian seasoning, and red pepper flakes. Cook for another minute.

Pour in the chicken or vegetable broth and add the Parmesan rind if using. Bring to a boil, then reduce heat to low and let it simmer for 10 minutes.

If using, stir in the fresh spinach or collard greens and let them wilt. Season with salt, pepper, and red wine vinegar if desired. Remove the Parmesan rind and bay leaf. Stir in the grated Parmesan cheese.

Ladle the soup into bowls and garnish with chopped parsley and additional Parmesan cheese if desired. Serve with crusty bread for dipping.