Cook the quinoa: In a medium saucepan, combine the rinsed quinoa and water or chicken broth. Bring to a boil, then reduce heat, cover, and simmer for 15 minutes or until the liquid is absorbed. Fluff with a fork and let it cool slightly.
Prepare the chicken: Preheat a grill or grill pan over medium-high heat. Brush the chicken with olive oil, oregano, garlic powder, salt, and pepper.
Grill the chicken for 6-7 minutes per side, or until fully cooked (internal temperature of 165°F / 74°C). Remove from heat and let rest for 5 minutes, then slice.
Make the salad: In a large bowl, combine the cooked quinoa, cherry tomatoes, cucumber, red onion, olives, feta cheese, and parsley
Whisk together lemon juice, olive oil, salt, and pepper, and pour over the salad. Toss gently to combine.
Top the salad with sliced grilled chicken and serve immediately, or refrigerate for up to 2 days.