In a large pot over medium heat, warm the olive oil and add the chopped onions, celery, and carrots. When onions are soft, add garlic and cumin. Stir and cook until garlic becomes aromatic then add tomatoes with its juice and lentils. Stir to combine. Add Parmesan rind and water. Increase heat and bring the mixture to a boil; cover the pot and reduce heat to a simmer.
Cook 30 minutes, or until the lentils are tender. Remove Parmesan rind. Add spinach and allow to wilt. Season with sea salt and freshly ground black pepper. Squeeze lime wedge over soup and stir. Spoon into bowls and sprinkle with freshly chopped parsley.
Recipe by The Culinary Chase at https://theculinarychase.com/2016/02/lentil-soup/