Prepare and cook the barley according to on-pack instructions until tender. Drain and set aside.
Pre-heat oven to 180°C. Spray a baking dish with cooking spray. Place the zucchini boats in the dish, sprinkle with herbs, salt and pepper and set aside.
Heat the oil in a frypan, add the onion and garlic and sauté gently until soft. Add the passata and mix well.
Combine the cooked barley with the passata mix and season to taste with salt and pepper.
Fill the zucchini boats with the barley mixture and top with shredded cheese. Bake for 30 minutes or until the zucchini is tender, cheese is melted and golden brown.
Sprinkle with parsley and serve.