Place sliced cucumbers on a layer of paper towels and sprinkle with a pinch of salt; let sit for 5 minutes to extract excess moisture, then pat dry.

In a medium mixing bowl, combine Greek yogurt, crumbled feta, chopped dill, lemon juice, garlic powder, and black pepper; whisk until the dressing is creamy and the feta is evenly distributed.

Add the dried cucumber slices to the bowl and fold gently using a spatula until every slice is thoroughly coated in the yogurt mixture.

Lay out four slices of bread and distribute the cucumber salad mixture evenly over two of the slices, stacking the cucumbers to create height.

Place the remaining slices of bread on top, press down gently to secure the filling, and slice diagonally with a serrated knife before serving.