In a medium saucepan, 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 all the liquid is absorbed. Remove from heat and let it sit, covered, for an additional 5 minutes.
Fluff the quinoa with a fork and let it cool to room temperature.
In a large mixing bowl, combine the diced cucumber, red bell pepper, cherry tomatoes, red onion, parsley, and mint.
Add the cooled quinoa to the bowl and mix well with the vegetables.
In a small bowl, whisk together the lemon juice, olive oil, salt, and pepper. Pour this dressing over the quinoa salad and toss gently until everything is well coated.
Taste and adjust the seasoning if necessary. If desired, sprinkle feta cheese on top for extra flavor.
Serve immediately, or refrigerate for about 30 minutes to allow the flavors to meld together before serving.