1. Rinse the quinoa under cold water.
2. In a saucepan, bring the water to a boil. Add the quinoa, reduce heat to low, cover, and simmer for 15 minutes or until the water is absorbed.
3. Remove from heat and let it sit, covered, for 5 minutes. Fluff with a fork.
4. In a large mixing bowl, combine the cooked quinoa, diced beets, arugula, feta cheese, and walnuts.
5. In a small bowl, whisk together the olive oil, lemon juice, minced garlic, salt, and pepper.
6. Pour the dressing over the salad and toss to combine.
7. Serve immediately or chill in the refrigerator for later.