Preparation Halve cucumber lengthwise and seed. Thinly slice cucumber and carrot crosswise. Thinly slice onion and transfer to a bowl with cucumber and carrot. In a small saucepan heat vinegar, sugar, and cayenne over moderate heat, stirring until sugar is dissolved. Cool vinegar mixture and pour over vegetables. Marinate salad at least 2 hours and up to 3 days.
Preparation Halve cucumber lengthwise and seed. Thinly slice cucumber and carrot crosswise. Thinly slice onion and transfer to a bowl with cucumber and carrot. In a small saucepan heat vinegar, sugar, and cayenne over moderate heat, stirring until sugar is dissolved. Cool vinegar mixture and pour over vegetables. Marinate salad at least 2 hours and up to 3 days.