1. Place potato on an aluminum foil-lined baking sheet. Coat potato with cooking spray; sprinkle with salt.
2. Bake at 450° for 40 minutes or until tender. Let cool 15 minutes.
3. Stir together yogurt and next 8 ingredients; reserve half of dressing.
4. 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.