Step 1: Begin by preparing your quinoa. Rinse 1 cup of quinoa under cold water using a fine-mesh sieve. In a medium saucepan, combine the rinsed quinoa with 2 cups of water or vegetable broth and a pinch of salt. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until all liquid is absorbed. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork and set aside to cool.
Step 2: While the quinoa cooks, prepare the chicken. Pat 2 boneless, skinless chicken breasts dry. In a shallow dish, whisk together 2 tablespoons olive oil, 1 tablespoon lemon juice, 1 clove minced garlic, 1/2 teaspoon dried oregano, salt, and black pepper. Add the chicken breasts, turning to coat. Marinate for at least 15 minutes, or up to 30 minutes in the refrigerator.
Step 3: Preheat your grill or grill pan to medium-high heat. Grill the chicken breasts for 5-7 minutes per side, or until cooked through and internal temperature reaches 165°F (74°C). Remove from grill, let rest for 5 minutes, then dice or slice into bite-sized pieces.
Step 4: Prepare the Lemon-Herb Vinaigrette. In a small bowl, whisk together 1/4 cup olive oil, 2 tablespoons fresh lemon juice, 1 tablespoon apple cider vinegar, 1 teaspoon Dijon mustard, 1 clove minced garlic, 2 tablespoons chopped fresh parsley, 1 tablespoon chopped fresh mint, and 1 tablespoon chopped fresh dill. Season with salt and pepper to taste.
Step 5: Assemble the salad. In a large bowl, combine the cooled quinoa, diced grilled chicken, 1 cup halved cherry tomatoes, 1/2 cup diced cucumber, 1/4 cup finely diced red onion, and 1/4 cup crumbled feta cheese (optional).
Step 6: Pour the Lemon-Herb Vinaigrette over the salad ingredients. Toss gently to combine, ensuring all components are evenly coated. Serve immediately or refrigerate for later.