Place the softened cream cheese in a medium mixing bowl.
Add the mayonnaise, chopped dill, lemon juice, lemon zest, garlic powder, onion powder, salt, and black pepper.
Mix until the spread is smooth and evenly blended.
Lay out the slices of crustless white bread on a clean surface.
Spread a generous layer of the cream cheese mixture over each slice of bread.
Arrange thinly sliced cucumber rounds in a single, even layer over half of the slices.
Place the remaining bread slices on top to form sandwiches.
Press gently so the layers hold together without squeezing out the filling.
Use a sharp knife to cut each sandwich into thirds or triangles.
Serve immediately or refrigerate for up to 4 hours before serving.