Thinly slice the cucumbers and red onion. If using regular cucumbers, you may want to peel them and remove seeds first.
In a small bowl or measuring cup, whisk together the white vinegar, olive oil, sugar, salt, and pepper until the sugar dissolves completely.
Place the sliced cucumbers and onion in a large mixing bowl.
Pour the vinegar dressing over the vegetables and toss gently until everything is evenly coated.
Stir in the chopped fresh dill.
Cover and refrigerate for at least 30 minutes before serving to allow flavors to develop.
Toss once more before transferring to a serving dish. Garnish with extra dill if desired.