1. Cook onion and sugar in hot oil in a large nonstick skillet over medium-low heat, stirring often, 15 to 20 minutes or until onions are caramel colored. Stir in garlic, and cook 1 more minute. Let cool 5 minutes; chop onions.
2. Stir together caramelized onion mixture, yogurt, and remaining ingredients in a medium bowl. Cover and chill 30 minutes or until ready to serve.