There is a restaurant right on the water in Port Royal that I've been to 3 or 4 times that serves your whole snapper on a platter, and it fills the platter. I don't remember the name because I was always with my driver, Huseph. Very local place - when you first walk in it doesn't look like a restaurant - walk onto the pier and there you are. I spent one of my birthdays there at night, with the gorgeous lights of Kingston across the harbor, filling my belly with some of the freshest fish I've eaten in Jamaica.