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

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

Drain cucumbers, pat dry, then fold into the yogurt-feta mixture.

Toast bread slices until golden and crisp, then let cool.

Spread cucumber filling on one slice of bread, add sprouts and onions, then top with another slice of bread.

Cut sandwiches diagonally and serve immediately for best freshness.