Dice the English cucumbers into small pieces, sprinkle with salt, and let sit in a colander for 15 minutes.

In a mixing bowl, combine plain yogurt and feta cheese, mash until smooth, then stir in herbs, lemon zest, lemon juice, and pepper.

Rinse the cucumbers under cold water after 15 minutes, pat them dry with paper towels.

Fold the cucumbers into the yogurt and feta mixture until evenly coated.

Assemble the sandwiches by layering sprouts, cucumber filling, and optional onion on bread slices.

Cut the sandwiches in half diagonally and serve immediately for best freshness.