Heat the olive oil in a large pot over medium heat. Add the leeks, carrots, celery and garlic and cook, stirring occasionally, until the leeks wilt, about 5 minutes. Add 2 cups water, the chicken broth, parmesan rind, lemon zest and pork bone. Bring to a simmer and cook until the vegetables are almost tender, about 15 minutes.
Remove the parmesan rind, lemon zest and pork bone from the pot with a slotted spoon. Bring the broth to a boil over medium heat. Add the tortellini, escarole and diced pork; season with pepper. Cook until the tortellini and escarole are tender, 4 to 5 minutes.
Adding a parmesan rind to soups and stews gives them rich flavor without a lot of fat.