Combine mayonnaise, sour cream, lemon juice, horseradish, dill weed, capers, if desired, and salt in a medium mixing bowl, stirring well. Add cucumber and tuna, stirring well. Cover and refrigerate until chilled.
Cut each tomato into 8 wedges, cutting to, but not through, base of tomato. Spread wedges apart to form shell. Spoon tuna salad into tomato shells. Place on a lettuce-lined serving plate. Serve immediately.
Oxmoor House Homestyle Recipes