Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius). lace onion in a shallow baking dish and sprinkle with sugar and vinegar. Bake for 15 minutes , or until onions are golden brown and softened . Remove from oven and allow to cool slightly.
In a medium-sized bowl, combine all ingredients, using a hand mixer or whisk to blend well.
Serve immediately , or store in an airtight container in the refrigerator .