Rinse the quinoa under cold water in a fine mesh strainer to remove any bitterness.
In a medium saucepan, combine the rinsed quinoa and water. Bring it to a boil, then lower the heat, cover, and simmer for 15 minutes until the quinoa is soft and the water is absorbed.
Remove the saucepan from the heat and let the quinoa rest, covered, for 5 minutes. Fluff with a fork and transfer to a large bowl to cool completely.
Mix the olive oil, lemon juice, minced garlic, dried oregano, salt, and black pepper in a small bowl while the quinoa cools. Put away.
After the quinoa cools, add cherry tomatoes, cucumber, red bell pepper, Kalamata olives, red onion, parsley, and mint to the bowl. Toss gently to combine.
Pour the dressing over the quinoa and vegetable mixture, tossing to coat evenly.
Gently fold in the crumbled feta cheese, if using.
Allow the salad to sit for at least 15 minutes for the flavors to meld, or refrigerate for an hour for the best flavor.
Taste and adjust the seasoning, if necessary, before serving.