Halve the cucumber lengthwise and scoop out the seeds with a spoon. Dice into small cubes. Place in a colander, sprinkle with salt, and let sit for 10 minutes. Pat dry with paper towels.
In a large bowl, combine the shredded chicken, diced cucumber, red onion, dill, and parsley.
In a small bowl, whisk together Greek yogurt, mayonnaise, lemon juice, garlic powder (if using), salt, and pepper until smooth.
Pour the dressing over the chicken mixture and stir gently until everything is evenly coated.
Taste and adjust seasoning with more salt, pepper, or lemon juice as needed.
Cover and refrigerate for at least 30 minutes before serving to allow flavors to meld. Serve cold.