Heat the oil in a large frying pan, add the chicken and onion and fry for 5 minutes, stirring until lightly browned.
Stir in the garlic and mushrooms and fry for 2 minutes, then mix in the barley. Add the red wine, half the stock and plenty of seasoning, then bring to the boil, stirring. Cover and simmer for 1 hour, topping up with extra stock as needed until the barley is soft.
Spoon into shallow bowls and garnish with the parsley and Parmesan. Serve with garlic bread and salad.