2) While the sauce is reducing, heat the butter in a separate oven-proof pan over a medium heat. Season the fish with salt and when the butter is melted, add the halibut to the pan. Cook for 2 minutes, flip over and then transfer the pan to the preheated oven and bake until cooked through, about 10 minutes.
3) Remove the sauce from the heat when reduced and stir in the olives and olive juice. To serve, divide the sauce equally among 4 dinner plates. Place the halibut (first caramelized side up) in the centre of each plate on top of the sauce. Place the avocado slices on top of the fish and garnish with a sprinkle of lime juice and coriander.