Combine first 8 ingredients, tossing to coat; cover and chill. Combine yogurt, juice, and horseradish, stirring well. Spoon about 1 1/2 tablespoons tuna mixture into each endive leaf. Drizzle each filled leaf with about 1/2 teaspoon yogurt mixture. Garnish with 1 tablespoon chives, if desired.
Wine note: The big-flavored meatiness of the tuna combined with the pizzazz of the capers and lime juice require a wine that is equally dramatic. My choice: Alsatian gewürztraminer. Bold, spicy, and aromatic, gewürztraminer also has a rich, almost lanolin-like texture that's superb with meaty fish. Try Domaine Weinbach Gewürztraminer 2002 (Alsace, France), $29. Powerful yet elegant litchi, spice, rose petal, and ginger aromas and flavors are followed by a texture that's silky and soft. -KM