Stir cream cheese, yogurt, chives, dill and ¼ teaspoon pepper together in a small bowl until well blended.
Spread the mixture evenly on 1 side of each bread slice.
Arrange cucumber slices and tomato slices in an even layer over the cream cheese mixture on 1 bread slice; sprinkle with salt and the remaining ⅛ teaspoon pepper.
Top with the remaining bread slice, cream cheese-side down.
Cut the sandwich in half diagonally.
