Crumble sausage into a 4 to 5-quart pan. cook over medium-high heat, stirring often, until lightly browned.
Add onion, garlic, thyme and pepper; cook, stirring often, until onion is light golden, about 6 minutes.
Rinse and sort beans, discarding any debris; drain. Add beans, broth and lemon peel to pan. Bring to a boil over high heat; then reduce heat, cover, and simmer until beans are tender to bite, about 2 hours.
Add carrots, celery and pasta to broth mixture. Bring to a boil over high heat; then reduce heat, cover, and simmer until vegetables and pasta are tender to bit, about 15 minutes.
To serve, ladle soup into bowls. Top with tomato and, if desired, sprinkle with cheese.