Heat grill to 230°C. Raw shuck the mussels using a blunt, flexible knife. Discard the top shell and place the half-shell mussels onto an oven tray. Combine the butter, lemon zest & juice, parmesan, parsley, garlic, salt and pepper. Spoon the butter mixture onto the mussels and sprinkle with panko breadcrumbs. Place under the hot grill for 4 – 5 min or until the topping turns golden brown. Sprinkle with fresh parsley and serve hot with a slice of lemon.