Add the olive oil to a large sauté pan over medium heat Add the pancetta, mushrooms, onion, celery and carrots. Cook until the vegetables soften, about 6 minutes. Add the garlic and rosemary, cook for 2 more minutes, stirring so the garlic doesn't burn.

Add the tomato paste and stir to mix into the vegetables. Stir in the chili flakes. Add the lentils and stock/broth and stir. Bring to a simmer, cover and cook for 30 minutes or until lentils are tender.

While the lentils cook bring a large pan of water to a boil. Cook the pasta according to package directions.

When the lentils are cooked, stir in the salt and and add more if needed depending on how salty your stock is (salt is added after as it can take longer to cook the lentils if you add salt first).

When the pasta is done, scoop out a cups worth of starchy water and set aside. Drain the pasta and add to the lentil sauce along with the Parmesan and mix well. If it is too dry, add a little of the pasta water or make it the consistency you like.

Serve topped with chopped parsley.