Cook the onions, carrots, and celery in oil over medium heat in a large skillet for 6-8 minutes or until translucent, stirring occasionally. Add in the mushrooms and garlic and cook another 5 minutes.
Stir in the lentils, crushed tomatoes, diced tomatoes, vegetable (or chicken) broth, tomato paste, and seasonings. Bring to a boil, reduce heat to low, cover, and simmer for 30 minutes until lentils are soft.
Meanwhile, cook pasta according to directions on box until al dente. Reserve 1/2 cup of the pasta water before draining.
Add the pasta water to the ragu sauce and then mix the pasta and ragu sauce together. Serve topped with parsley and parmesan.