Wash and dice the English cucumbers, sprinkle with salt and let sit for 10 minutes in a colander to remove moisture.

In a mixing bowl, combine yogurt, crumbled feta, chopped herbs, lemon zest, lemon juice, and pepper until creamy.

Pat cucumbers dry with paper towels, then fold into yogurt mixture and mix thoroughly.

Lay out bread slices, spread cucumber filling on one slice, add sprouts and onions if desired, top with another slice.

Cut each sandwich in half diagonally and serve immediately for best freshness.