Place the red onion in small bowl and cover with cold water. Let it sit for about 5 minutes to make the onion less pungent, and then drain and dry the onion with paper towel.
Combine the cucumber, shredded cabbage, red onion, olive oil, Greek yogurt, lemon juice, sugar, fresh dill and salt in a bowl. Stir well and then season with freshly ground black pepper. Chill until ready to use.