In a saucepan cover potatoes with water by 1 inch and simmer until tender, 15 to 20 minutes.
Transfer potatoes with a slotted spoon to a colander to drain and cool 10 minutes.
Return water in pan to a boil and blanch snap peas until crisp-tender, 1 – 2 minutes. Place snap peas in colander and refresh under cold water. Drain snap peas and pat dry with paper towels.
Cut potatoes lengthwise into quarters. In a bowl toss together potatoes, snap peas, green onion, vinegar, oil, mint, and salt and pepper to taste.