1. Add cream cheese, lemon zest and juice, dill, and chives to a bowl. Mix to combine.
2. To make whitefish salad: Whisk mayonnaise with lemon zest and juice until combined. Add whitefish, celery, and onions, and mix gently until combined. Season with salt and freshly ground black pepper. Cover and refrigerate for at least one hour before serving.
3. To serve: Scatter arugula or watercress on a large platter. Loosely fold lox and place over greens. Add bowls of cream cheese, whitefish salad and capers, then fill in empty areas with red onion, vine tomatoes, fresh dill and lemon wedges.