Sauté the Bacon and Vegetables:
Heat olive oil in a large soup pot (or Dutch Oven) over medium-high heat. Add the bacon (if using) and cook for about 3 minutes, stirring often. Then add the carrots, celery, onions, garlic, Italian seasoning, and red pepper flakes. Cook for 5 minutes, or until the onions are soft and translucent. Season lightly with salt and pepper.

Cook the Tomato Paste: Push the vegetables to the sides of the pot to create a small space in the center. Add the tomato paste and stir it constantly for 1 minute to caramelise it slightly. This step deepens the flavour. Then stir the tomato paste into the vegetables.

Simmer the Soup Base: Pour in the broth, diced tomatoes, and add the bay leaf. Stir well, scraping up any browned bits from the bottom of the pan. Bring the soup to a gentle boil, then reduce the heat to medium-low and let it lightly simmer for 30 minutes.

Cook the Tortellini and Wilt the Spinach:
Turn the heat up to medium and add the tortellini. Cook according to the package instructions until al dente (typically 2-3 minutes). Add the spinach and stir until wilted, about 1 minute. If the soup is too thick, add more broth until your desired consistency is achieved.

Finish and Serve:
Remove the bay leaf and taste the soup. Adjust the seasoning with salt and pepper, if needed. Ladle the soup into bowls, season with freshly ground black pepper, and top with shaved or grated Parmesan, if desired. Serve warm and enjoy!