For those who relish creativity and sophistication in their meals, the unexpected twists of oranges and fennel satisfy. You’ll never think of tuna salad the same way again!
Toss together apple and 1½ tablespoons lemon juice; set aside.
Place ½ tablespoon lemon juice, olive oil, vinegar, mustard and sugar in a blender or food processor and process until smooth. Season with salt and pepper.
Arrange arrange radicchio, fennel, orange, grapefruit and onion on a serving platter or salad plates. Top with tuna and drizzle with dressing; serve immediately.