Dice the English cucumbers into small pieces, then place them in a colander. Sprinkle salt over the cucumbers and let them sit for at least 15 minutes.

In a mixing bowl, combine yogurt, crumbled feta cheese, fresh herbs, lemon zest, lemon juice, and pepper, mixing until smooth.

After 15 minutes, drain the cucumbers and pat them dry with paper towels.

Add the drained cucumbers to the yogurt mixture and stir until well-coated.

Toast the slices of bread until golden brown. Assemble the sandwiches with sprouts, cucumber salad mixture, and sweet onion if desired.

Cut each sandwich in half diagonally and serve immediately.