Place potato on an aluminum foil-lined baking sheet. Coat potato with cooking spray; sprinkle with salt.
Bake at 450 for 40 minutes or until tender.
Let cool 15 minutes.
Stir together yogurt and next 8 ingredients; reserve half of dressing.
Combine potato and onion in a large bowl; add remaining dressing, tossing gently to coat. Cover and chill 2 hours. Toss with reserved dressing just before serving.