Rinse quinoa under cold water. In a saucepan, bring 2 cups of water to a boil, add quinoa, reduce heat to low, cover, and simmer for 15 minutes or until water is absorbed. Fluff with a fork and let it cool.
While the quinoa is cooling, chop the tomatoes, cucumber, onion, and olives.
In a large bowl, combine quinoa, vegetables, olives, and feta cheese.
In a small bowl, whisk together lemon juice, olive oil, salt, and pepper. Pour over the salad and toss to combine.
Garnish with fresh parsley. Serve chilled or at room temperature.