Embarrassingly easy to make, this crisp, tart, tangy salad is an Eastern European Jewish staple. It takes about 5 minutes to prepare, which makes it a perennial favorite at my house.
Wash the cucumber. Partially remove the peel in lengthwise strips, using a vegetable peeler, leaving a little skin between each strip. (This gives you pretty green stripes on the cucumber slices.) Thinly slice the cucumber widthwise. Thinly slice the onion and break into rings.
Place the vinegar, sugar, salt, and pepper in a bowl and whisk until the su