In a large stockpot over low heat, warm the olive oil. Add the garlic and cook for 1 minute. Add the leeks, cover, and cook, stirring once or twice, for 6 minutes. Add the carrots, parsnip, celery, zucchini, rosemary, and half of the parsley and season with salt and pepper. Turn the heat to medium and cook, stirring, for 5 minutes. The vegetables should be just beginning to turn gold. Add the tomato paste, stir to coat the vegetables, and cook another 2 minutes. Add the tomatoes, Parmesan rind (if using), beans, and potatoes (if using) and stir well. Turn the heat to high, add the stock, and bring to a boil. Turn the heat to low, add the red chili flakes, and simmer, partially covered, for 15 minutes. Taste and adjust the seasoning, adding more salt and pepper if needed. If the soup is not as flavorful as you like, remove the lid and simmer it over medium heat for another 10 minutes.