This recipe inspired by chef Joshua McFadden, of Portland, Oregon's Ava Gene's, plays fast and loose with convention. Northern Italian tonnato, a silky, savory sauce made with tuna, typically is served with veal. But we like to balance the puree's rich, meaty flavor with sweet snap peas and peppery radishes; flaked tuna tops off the salad. Asian fish sauce may be a surprise ingredient, but just a couple teaspoons of it bolsters the flavor of the tuna.