Heat oil in 6-quart pot over medium-high heat. Cook and stir onion for 3 to 5 minutes or until softened and translucent. Add carrot, celery, and garlic. Cook, covered, stirring occasionally, for 5 minutes or until the carrot is softened. Add the 12 cups broth, the lentils, basil, thyme, and salt. Bring to boiling. Reduce heat to low; add kale. Cook 30 to 35 minutes or until lentils are tender, adding additional broth if necessary. Stir in lemon juice and top with grated peel before serving.