Add the capers and the lemon slices to the pan. Remove the pan from the heat and immediately add the butter, parsley, 1/1.5/2 tbsp of lemon juice and 0.5/0.75/1 tsp of lemon zest. Whisk until the sauce begins to thicken. Return the seabass to the pan. Season with a pinch of black pepper. Plate the root veg mash and serve the seabass and sauce to the side.