Rinse the quinoa under cold water in a fine-mesh sieve to remove the natural bitterness.

In a medium saucepan, combine the rinsed quinoa and water (or vegetable broth). Bring to a boil, reduce heat to low, cover, and simmer for about 15 minutes or until the liquid is absorbed.

Fluff the cooked quinoa with a fork and let it cool.

While the quinoa is cooling, chop the cherry tomatoes, cucumber, bell pepper, and red onion. Place them in a large mixing bowl.

In a small bowl, whisk together olive oil, lemon juice, salt, and pepper until well combined.

Add the cooled quinoa to the bowl with the chopped veggies, pour the dressing over and toss everything gently until well mixed.

Sprinkle fresh parsley and feta cheese (if using) on top. Serve chilled or at room temperature.