1. Spray a 6-quart saucepan with non-stick spray and set over medium-high heat. Add the sausage and cook, breaking it up with a wooden spoon, until browned, 4-5 minutes. Stir in the onion, celery, carrot, and garlic; cook, stirring occasionally, until the onion begins to brown, about 5 minutes. Add the tomatoes, bring to a boil, reduce the heat to medium, and simmer for 10 minutes.
2. Stir in the lentils, broth and pepper; bring to a boil. Reduce the heat and simmer, covered, until the lentils are tender, about 30-40 minutes.