1. Heat the olive oil in a large pot over medium heat. Add the onion, garlic and red pepper flakes and cook, stirring occasionally, until the onion is slightly soft, about two minutes. Remove 1 Tbsp. of the flavored oil and set aside. Add the tomato paste and cook, stirring, two more minutes. Add the chicken broth, 4 cups water and the cheese rind, if using. Bring to a boil, then add the pasta and cook, stirring occasionally, 5 minutes. Add the lentils along with the liquid from one of the cans, reduce the heat to medium-low and simmer until the pasta is tender, 10-12 more minutes.
2. Meanwhile, whisk 1 Tbsp. parsley and 1 Tbsp. water into the reserved flavored oil. Stir 1/4 cup parmesan and the remaining parsley into the soup, remove the cheese rind if using and add salt to taste. Ladle into bowls, drizzle with the flavored oil and top with remaining 1/4 cup parmesan. Serve with bread if desired.