Bring the water to a boil, add the quinoa and a pinch of salt, cover, and simmer for 15 minutes. Fluff and spread on a plate to cool completely.

Whisk together the lemon juice, olive oil, Dijon mustard, honey, salt, and pepper until smooth.

Core and dice the apple, thinly slice the celery, and finely chop the red onion. In a large bowl, combine the cooled quinoa, apple, celery, onion, cranberries, and walnuts.

Pour the dressing over the salad, toss to coat, then sprinkle with parsley and toss once more. Serve right away or let it sit for 10 minutes.