Combine oil and garlic in a large bowl; set aside.
Cook potatoes in boiling salted water to cover 15 to 20 minutes or until tender; drain potatoes, and place in a large bowl.
Whisk vinegar and next 3 ingredients into oil mixture. Pour over warm potatoes, tossing to coat. Cover and chill 8 hours.
Combine potato mixture, mayonnaise, and green onions, tossing gently.