Special equipment: Special equipment: a 2-inch round cookie cutter
In a medium bowl, combine the cream cheese, chopped chives, horseradish, pepper, salt, capers and lemon zest until smooth.
Arrange 4 bread slices on work surface. Spread 2 tablespoons of the cream cheese mixture over each bread slice to cover. Lay the watercress in an even layer on top. Top with smoked salmon. Using a 2-inch round cookie cutter, cut 3 or 4 circles out of each slice of bread. Place a dollop of the cream cheese mixture on top and garnish with 2 pieces of chive.
Arrange the sandwiches on a platter and serve.