Soak lentils in water overnight, then reserve the liquid for cooking.
Heat olive oil in a large stock pot over medium heat. Sauté onion, carrots, and celery until softened. Add sausage and cook through, breaking apart with a wooden spoon. Add leek, cumin, clove, and bay, cooking briefly to bloom spices. Add lentils and soaking liquid, then season to taste. Cook until lentils are soft, 60–90 minutes.