Rub half the oil into salmon and season well. Mix together olives, garlic, capers and remaining oil.
Cook salmon on a preheated barbecue plate, skin side down, for 5 mins. Turn and cook for a further 2 mins, for medium. Cook olives, garlic and capers on hot plate, stirring, for 2-3 mins, until garlic is golden.
Meanwhile, heat wine and vinegar in a small pan on high until boiling. Boil for 5 mins, or until reduced by half. Reduce heat to medium. Add butter, one piece at a time, whisking constantly until all butter is incorporated and sauce is glossy. Remove from heat. Stir through parsley.
Top salmon with olive mixture. Spoon sauce over salmon to serve.