Add sugar, fish sauce, and water to the skillet. Over medium heat, cook the mixture for about 5 minutes, until it starts to turn brown and there are large bubbles throughout. Sprinkle in the pepper and the cooked shallots and cook for a minute more. Add the fish and cook, turning gently with a spatula every three minutes or so, until it is coated evenly with thickened caramel sauce, and just cooked through, 8-10 minutes. (you can add a few tablespoons of water, 1 tablespoon at a time, if the pan seems too dry)