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

In a mixing bowl, combine yogurt, crumbled feta cheese, and fresh herbs. Add lemon zest, lemon juice, and pepper, then mix well.

After 15 minutes, pat cucumbers dry with paper towels and fold them into the yogurt mixture.

Toast bread slices until golden brown and allow to cool slightly.

Spread cucumber filling onto one slice of bread, layer with sprouts and onion slices if desired, then top with another slice of bread.

Cut each sandwich in half diagonally and serve immediately.