In a medium pot, bring the water or vegetable broth to a boil. Add the rinsed quinoa, reduce the heat to low, cover, and simmer for about 15 minutes or until the quinoa is fluffy and all the liquid is absorbed.
Once cooked, remove from heat and let it sit covered for 5 minutes before fluffing it with a fork. Allow the quinoa to cool to room temperature.
In a large mixing bowl, combine the cherry tomatoes, cucumber, red bell pepper, red onion, Kalamata olives, feta cheese (if using), parsley, and mint.
In a small bowl, whisk together the olive oil, lemon juice, dried oregano, salt, and pepper. Pour this dressing over the salad ingredients.
Add the cooled quinoa to the bowl and toss everything gently until well combined and evenly coated with the dressing.
Taste and adjust seasoning if necessary, then let the salad sit for at least 15 minutes to allow the flavors to meld together.