Make the Cream Cheese Spread: In a small bowl, use a hand mixer to blend the softened cream cheese and mayonnaise until the mixture is smooth.
Season the Spread: Stir the chopped fresh dill, chopped chives, garlic powder, salt, and black pepper into the smooth cream cheese mixture until evenly combined.
Spread the Bread: Apply an even layer of the cream cheese mixture to one side of each bread slice.
Slice the Cucumber: Thinly slice the English cucumber, keeping the slices thin enough to layer neatly onto the bread.
Add the Cucumber: Arrange the cucumber slices over half of the prepared bread slices, adding extra herbs on top if desired.
Assemble the Sandwiches: Place the remaining bread slices over the cucumber-topped slices to form the sandwiches.
Trim the Crusts: Remove the bread crusts if they have not already been removed.
Cut the Sandwiches: Cut each assembled sandwich into 3 pieces for serving.
Serve or Store: Serve the cucumber sandwiches immediately, or cover and refrigerate them for up to 24 hours.