Place one fish skin-side uppermost on work surface and press thumbs firmly along backbone; turn fish over, pullout backbone from head and cut free at tail. Repeat with remaining fish.

Lay fish in a shallow, non-metallic dish. Sprinkle over sea salt, vinegar, garlic and onion. Cover and leave in a cool place over- night..

Drain and rinse fish; reserve some of onion. Dry fish on absorbent kitchen paper, and then place on a serving plate. In a small bowl, mix together oil, lemon juice, reserved onion, salt, and pepper. Pour over fish and garnish with diced red pepper (capsicum) and parsley.