Dice two English cucumbers into small pieces. Place them in a colander, sprinkle salt over them, and let sit for 10 minutes.

In a large mixing bowl, combine Greek yogurt and crumbled feta cheese. Add chopped herbs, lemon zest, and juice. Season with pepper and mix well.

Pat the drained cucumbers dry with paper towels to remove excess moisture.

Fold the dried cucumbers into the yogurt mixture until well coated.

Toast slices of bread until golden. On one slice, layer sprouts or vegetables and spread the cucumber filling on top. Add onion slices if desired.

Cut the sandwiches in half diagonally and serve immediately.