1. Using a knife, peel and slice mushrooms very thinly. Peel onion and dice very finely.
2. In a pan, bring chicken stock to the boil; add seasoning.
3. Put in sliced mushroom and onion and gently boil for 20 mins.
4. Using a knife, cut chicken into 1/4 inch dice; put in to the soup and simmer for 5 to 10 mins.
5. Serve hot in a heated tureen with some croutons if you like.