Marinate the chicken by mixing olive oil, garlic powder, onion powder, oregano, salt, and pepper. Brush over chicken breasts and let marinate for at least 30 minutes.
Preheat grill or stovetop grill pan over medium-high heat. Grill chicken for 6-7 minutes on each side until internal temperature reaches 165°F. Let rest for 5 minutes before slicing.
In a large bowl, combine cooked quinoa, cherry tomatoes, cucumber, red onion, feta cheese, olives, and parsley. Toss gently to combine.
Assemble the bowl by placing quinoa and vegetable mixture in each bowl, topping with sliced grilled chicken and drizzling with lemon juice.