Place snow peas in a bowl and cover with boiling hot water. After 2 minutes, strain and shock in an ice bath. When cool, strain. Cut snow peas on the diagonal into 1/2-inch diamond shapes, discarding end pieces.
In a me dium-sized bowl, combine snow peas, scallions and radishes. In a separate bowl, whisk together vinegar and oil. Pour over vegetable mixture and serve.