In a medium saucepan, combine the quinoa and water. Bring the water to a boil, reduce the heat to low and cover. Cook until all of the water is absorbed, 15 to 20 minutes. Fluff the quinoa with a fork.
Transfer the cooked quinoa to a large baking sheet and spread it out evenly. Let it cool to room temperature.
Transfer the quinoa to a medium-sized bowl and add the tomatoes, cucumber, olives and feta cheese. Stir gently to combine.
In a small bowl, whisk together the olive oil, red wine vinegar, dried oregano, salt and pepper. Pour the dressing over the quinoa salad and stir to combine. Serve