Wash cucumbers thoroughly under cold water, slice thinly, sprinkle with salt, and let sit for 15 minutes. Rinse and pat dry.
In a medium bowl, combine softened cream cheese and mayonnaise, blend until smooth, then add dill, garlic powder, and lemon juice. Mix well.
Spread cream cheese mixture on one side of each slice of bread, layer cucumber slices on half of the bread slices, top with remaining slices, cream cheese side down.
Chill sandwiches for up to 1 hour before serving, then cut into quarters or halves and arrange on a platter.