In the bottom of a large salad bowl, whisk together vinegar, oregano, salt and pepper. Continue whisking while you add olive oil in a slow steady stream; whisk until emulsified. Add more salt and pepper to taste.
Add quinoa, and next 8 ingredients (tomatoes through feta) to bowl; gently toss to coat and combine. Serve.
Note that preparation time does not include cooking quinoa or allowing it to cool. Always rinse quinoa until the water runs clear before cooking.
This salad travels well and holds up for a few days in the refrigerator - perfect for weekday desk lunches!
The dressing for this salad is essentially a half recipe of Greek Salad Dressing, a staple in our house!