- 1 1/2 cups quinoa (any color) rinsed well
- 4 teaspoons kosher salt plus more
- 1 medium red onion, sliced 1/4″ thick
- 1/2 cup apple cider vinegar
- 3 tablespoons sugar
- 2 large ripe firm peaches, cut into 1/2″ pieces
- 1/2 bunch arugula, thick stems trimmed, leaves torn (about 2 cups)
- 2 cups small cherry tomatoes (about 1 pint), halved
- 1/4 cup olive oil
- 1/2 cup 1/2″ pieces chives, divided
- Freshly ground black pepper
- Bring quinoa and 4 cups water to a boil in a medium saucepan. Season with salt. Cover, reduce heat, and simmer until quinoa is tender, 8-10 minutes. Drain, return quinoa to pan, and cover. Remove from heat and let sit 15 minutes. Fluff with a fork and spread out on a rimmed baking sheet; let cool.
- Meanwhile, place onion in a small bowl. Bring vinegar, sugar, and 4 teaspoon salt to a boil in a small saucepan, stirring to dissolve sugar and salt. Pour over onion and let stand 20 minutes. Drain, reserving pickling liquid.
- Toss pickled onion, peaches, arugula, tomatoes, oil, 1/4 cup chives, and 3 tablespoons reserved pickling liquid in a large bowl; season with salt, pepper, and more pickling liquid, if desired. Fold in quinoa.
- Serve salad topped with remaining 1/4 cup chives.
- DO AHEAD: Quinoa salad can be made 6 hours ahead (do not add arugula and chives). Cover and chill. Bring to room temperature and toss in arugula and chives just before serving.