Heat vinegar in a small saucepan over high heat until boiling. Add onion and cook, turning as needed, until it's pink and most of vinegar is absorbed, about 5 minutes. Spoon onion out of pan, let cool slightly, then roughly chop.
Mix remaining ingredients in a large bowl. Add onion and toss just to combine.
Servings 0
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.