Rinse the quinoa thoroughly in a fine-mesh sieve. In a medium saucepan, combine the rinsed quinoa and 2 cups of water. Bring to a boil, then reduce the heat to low, cover, and simmer for 15 minutes, or until the water is absorbed. Remove from heat and let it stand, covered, for 5 more minutes to steam. Fluff with a fork and spread on a baking sheet to cool completely.

While the quinoa cooks and cools, prepare your vegetables. Dice the cucumber, halve the cherry tomatoes, finely dice the red onion, and chop the parsley. Add them all to a large salad bowl along with the rinsed and drained chickpeas.

In a small bowl or a jar with a lid, combine the olive oil, fresh lemon juice, Dijon mustard, minced garlic, salt, and pepper. Whisk or shake vigorously until the dressing is well combined and emulsified.

Once the quinoa is completely cool, add it to the large bowl with the vegetables. Pour the vinaigrette over the top, add the crumbled feta, and gently toss everything together until well combined. Serve immediately or chill for later.