Peel and slice cucumbers into thin slices.
Cut onion in half and cut into very thin slices.
Combine onions and cucumbers in a large bowl.
In a separate, medium-sized bowl, combine remaining ingredients. Stir until sugar dissolves.
Pour vinegar mixture over cucumbers and onions. Stir until the cucumbers are evenly coated in the dressing.*
Refrigerate at least 20 minutes. Before serving, drain liquid and place in a serving bowl to serve.