Wash cucumber and cut lengthwise thin slices from the middle.
Mash trout fillets finley with a fork, stir in horseradish and season to taste with pepper,
and lemon juice. Cover cucumber slices with trout-mixture and roll up.
Secure with wooden skewers.
Brush pumpernickel slices with butter and top with some lettuce. Place cucumber rolls upon. Garnish with tomatoes and chives.