Rinse 1 cup of dry quinoa under cold water, then combine with 1 3/4 cups of water in a saucepan. Bring to a boil, reduce to a simmer, cover, and cook for 12 minutes until the water is absorbed. Fluff with a fork and set aside to cool for 5–10 minutes before using.
While the quinoa cooks, dice the cherry tomatoes, mini cucumbers, red onion, and kalamata olives. Roughly chop the arugula into bite-sized pieces.
In a small bowl, whisk together the red wine vinegar, extra virgin olive oil, dried oregano, salt, and pepper. Taste and adjust seasoning. Or option to add right to the bowl.
Add the slightly cooled quinoa to a large bowl along with the arugula, cherry tomatoes, cucumbers, red onion, and kalamata olives. Pour the dressing over the top and toss well until everything is evenly coated.
Crumble the feta cheese generously over the top. Taste for seasoning — add a pinch more salt, pepper, or a splash more red wine vinegar if needed. Serve immediately or refrigerate until ready to eat.
