Flatten the lamb by pressing on it and place in a large dish.
Sprinkle over the onion.
Mix together the balsamic vinegar, Perry vinegar, olive oil, lemon juice and sugar. Season with the salt and pepper and pour over the lamb.
Leave to marinate for 1 hour, turning frequently to ensure an even coating.
Remove the lamb from the marinade and place on a medium-hot BBQ and cook for 30 - 35 minutes, turning occasionally and basting with the reserved marinade.
For the garlic, take a bulb of new season, green garlic and shake over some olive oil. Add a couple of sprigs of fresh thyme and then wrap loosely in some tin foil. Leave over the warm part of the barbecue for 30 minutes or until soft. Remove and enjoy this delicious meal in your lovely barbeque lodge.