Place the potatoes in a medium saucepan and cover with cold water. Place over high heat and bring to the boil. Cook, covered, for 15 minutes or until tender. Drain potatoes and set aside for 5 minutes to cool slightly. Cut into 1cm-thick slices and place in a bowl. Add the oil, mustard and capers and gently toss to combine. Season with salt and pepper.
Meanwhile, combine the cucumber, vinegar, salt and sugar in a small bowl and set aside for 10 minutes to develop the flavours.
Combine the prawns and chopped dill in small bowl.
Arrange the potato salad, cucumber salad, prawns, salmon, bread and lettuce on serving plates or platter.