Combine cucumbers, red onion, and dill in a medium bowl.
In a small bowl, whisk together vinegar, olive oil, salt, and pepper.
Pour dressing over cucumber mixture and toss to combine.
Refrigerate for at least 30 minutes before serving to allow flavors to meld.
Notes
For a creamier salad, add a dollop of plain Greek yogurt or sour cream to the dressing. You can also add other vegetables like bell peppers or tomatoes.