Wash the cucumbers under cool running water and thinly slice them into rounds. Place in a colander and sprinkle half of the salt over them. Let rest for 10-15 minutes.

In a medium mixing bowl, combine Greek yogurt, mayonnaise, olive oil, lemon juice, minced garlic, fresh dill, remaining salt, black pepper to taste, and optional sugar. Whisk until smooth.

Pat the cucumbers dry with paper towels. Add the cucumbers and red onion to the dressing and gently stir to coat evenly.

Transfer the salad to a serving bowl or airtight container. Refrigerate for at least 20 minutes before serving.

After chilling, stir gently and serve cold, optionally garnished with additional dill.