Add vinegar, Dijon mustard, honey, salt, and pepper to a jar with a lid and shake well to mix. Add onion; let pickle for 30 minutes. Do Ahead: Onions can be pickled up to 24 hours in advance. Refrigerate if not using right away.
Stir together cucumber and dill in a bowl; drain excess water. Toss salad with dressing and onions just before serving.
Editor's note: The recipe was first printed online in June 2014. Head this way for more of our favorite ways to use cucumbers →
