Coat a large heavy saucepan with cooking spray and heat on medium high. Add the onion and sauté with some seasoning for 5 mins or until the onion is translucent (if the pan starts to look too dry, you can add a bit more cooking spray).

Add the garlic and cook another minute.

Add the mushrooms and saute until the liquid is released and evaporates.

Raise the heat to high, add the barley, coat with the mushroom mixture and cook for another minute.

Pour in the wine and stir until it is absorbed and the alcohol has cooked down. Stir 4 cups of the stock and parsley. Cover, lower the heat to low and cook for 40 mins on a slow simmer until the barley is tender (stirring occasionally and adding remaining stock if it looks dry). Remove from the heat and stir in the grated Parmesan cheese (if using).

Taste and season with salt and pepper to taste.

Serve immediately.