In your slow cooker, combine diced onion and minced garlic. Pour in the vegetable broth and undrained diced tomatoes, then sprinkle in dried basil, oregano, and ground black pepper. Stir everything together.

Cover the slow cooker and set it to cook on low heat for 4 hours or on high heat for 2 hours.

Once the vegetables are tender, stir in the cheese tortellini and chopped spinach. Switch to high heat if it was on low, and let it cook for an additional 30 minutes.

After the tortellini has cooked, stir in the heavy cream and grated Parmesan cheese. Adjust seasoning with salt and pepper as needed.

Ladle the soup into bowls and garnish with fresh basil or parsley. Serve hot.