1 medium yellow onion; peeled, sliced thin
3 medium cucumbers; thinly sliced
1 cup water
1/2 cup white vinegar
1/2 cup sugar
1/2 teaspoon celery; fennel, or mustard seed
Salt; as desired
Place onion and cucumber in a bowl.
In a saucepan, combine salt (if desired), water, vinegar and sugar, heating slightly to dissolve sugar.
Pour over onion and cucumber.
Chill and serve.