Peel the cucumber and cut it in half lengtwise, then in half again, then cut into slices of desired thickness. (by all means, don't throw away those peels, munch on 'em while fixing this salad!)
Add cucumber, yogurt, half the walnuts, za'atar, salt and pepper to a medium mixing bowl and mix well.
Arrange the leafy greens at the bottom of a plate and add cucumber salad on top.
Garnish with the rest of the walnuts and young sprouts if desired