In a skillet, cook Pancetta over medium heat until golden on all sides, stirring often.
Remove with slotted spoon and set aside. Add onion and garlic to skillet and cook until onion is softened.
Spoon the mixture into the BLACK + DECKER™ 7-QUART Slow Cooker stoneware pot. Add Pancetta and remaining ingredients, except celery leaves.
Cover and cook on HIGH for 4-5 hours or LOW for 8-10 hours, until lentils are very tender. Stir in celery leaves.