Slice cucumber into 1/8-inch rounds. Lay on double paper towels, sprinkle evenly with 1/2 tsp salt. Rest 15 minutes until moisture beads on surface.
Combine softened cream cheese, mayo, dill, chives, lemon juice, garlic powder, salt, and pepper. Beat until smooth. Refrigerate until ready to use.
Press fresh paper towels firmly onto each cucumber slice. Flip and press again. All surface moisture must be removed before assembly.
Remove crusts from all 12 bread slices using a sharp serrated knife. Cut in one clean motion for neat edges.
Spread cream cheese generously on BOTH slices of bread per sandwich, reaching edge to edge, corner to corner.
Layer 4 to 5 dried cucumber slices on one cream cheese-covered slice. Overlap slightly. Top with second slice and press gently. Repeat for all 6 sandwiches.
Cut each sandwich diagonally into 2 triangles (or 4 rectangles for finger size). Plate immediately or refrigerate covered with plastic wrap up to 4 hours before serving.
