Wash the porcini and cook on low heat in 2 litres of water for about 30 minutes. Cook the pasta in plenty of boiling salted water for about 10 minutes until al dente. In the meantime, clean and wash the soup vegetables and cut them into thin strips or rings.
Remove the mushrooms from the cooking water and put them aside. Add vegetables and pepper to the mushroom water and cook for about 10 minutes. Cut the mushrooms into strips. Drain the noodles and add to the soup together with the mushrooms.
Season soup with lemon juice and salt. Wash parsley, dab dry, chop and sprinkle over the soup.