Cook quinoa according to package instructions. Set aside to cool completely. (Pro tip: for quicker cooling, transfer cooked quinoa to a shallow bowl and refrigerate, stirring occasionally, until completely cool.)
Chop the cucumber, tomato, onion, and peppers into uniform pieces.
Prepare the dressing by combining olive oil, lemon juice, white wine vinegar, garlic, Greek seasoning, salt & pepper in a medium jar with a lid. Seal tightly and shake vigorously to combine.
In a large mixing bowl, combine the cooled quinoa, chopped veggies, kalamata olives, garbanzo beans, feta, and dressing.
Enjoy immediately or refrigerate for later!