This healthy fish recipe from chef mike lata is made with banded rudderfish, which is an amberjack--a species coveted in sushi restaurants, where it's known by its japanese name, hamachi. Lata's love affair with the italian dish vitello tonnato (cold sliced veal with tuna sauce) started with a glorious one he had in milan. He's found the sauce to be a great way to use the scraps that result from butchering whole fish. He serves thicker versions over cold poached meats and thinner ones like this over vegetables and salads.