Marinate the chicken by combining olive oil, garlic powder, onion powder, oregano, paprika, salt, and pepper. Rub the mixture on the chicken and let it marinate for at least 15 minutes.
Preheat the grill or grill pan over medium-high heat. Grill the marinated chicken for 6-7 minutes on each side until it reaches an internal temperature of 165°F. Let it rest for 5 minutes before slicing.
Prepare the tzatziki sauce by mixing Greek yogurt, grated cucumber, minced garlic, lemon juice, salt, and pepper in a bowl. Refrigerate until ready to serve.
Assemble the bowl by dividing cooked quinoa among four bowls, topping with sliced chicken, cherry tomatoes, cucumber, red onion, feta cheese, and parsley. Drizzle tzatziki sauce over each bowl.