Put the chestnuts, parsley, lemon juice and garlic in a blender, then whizz until you get a course paste. Keep on pulsing and gradually add the oil. Then stir in the grated cheese and season with salt and pepper. Set aside.
Finely slice the mushrooms, then heat some oil in a frying pan and sauté them.
Meanwhile, cook the pasta until al dente, following the instructions on the packaging. Drain and mix with the mushrooms and chestnut pesto.
Sprinkle with some extra grated cheese and chopped herbs. Serve warm.