1. Bring first 3 ingredients and 2 cups water to a boil in a large saucepan over medium-high heat, and cook 20 minutes or until tender. Drain and let cool 30 minutes.
2. Whisk together yogurt and next 6 ingredients in a large bowl until combined.
3. Gently fold potatoes into yogurt mixture. Cover and chill 1 to 12 hours. Garnish, if desired.