Heat the oil in a heavy large pot over medium heat. Add the onion, carrots, celery, garlic, salt and pepper and saute until tender, 5 to 8 minutes.
Add the tomatoes with their juices and simmer, stirring occasionally, until they break down, about 8 minutes.
Stir in the lentils, then the broth and thyme. Bring to a boil, then cover and simmer over low heat until the lentils are almost tender, about 30 minutes.
Stir in the pasta and simmer until al dente, about 8 minutes. Season, and serve sprinkled with Parmesan and drizzled with olive oil.