Slice the cucumbers into thin rounds or ribbons and place them in a large bowl.
Thinly slice the onion and add it to the cucumbers.
In a small bowl, mix sour cream, lemon juice, crushed garlic, chopped dill, salt and black pepper until smooth.
Adjust the dressing with a little extra lemon or sour cream if needed so it is creamy and pourable.
Just before serving, pour the dressing over the cucumbers and onion.
Toss gently until all slices are lightly coated.
Taste and adjust seasoning, then serve immediately while crisp and cool.