Make dressing: Whisk together Greek yogurt, sour cream, lemon juice, finely chopped dill, garlic powder, salt, and pepper in a medium bowl. Taste and adjust seasonings. Set aside.
Slice cucumbers into rounds, then cut into half rounds. Salt cucumbers by laying out sliced cucumbers and sprinkling with salt, waiting about 10 mins, and then patting them dry.
Slice red onion thinly. Add to large bowl with roughly chopped dill.
Toss: Pour dressing over cucumber mixture and toss to coat evenly.
Serve immediately or chill up to 2 hours before serving.
