Marinate the chicken by mixing olive oil, garlic powder, onion powder, oregano, paprika, salt, and pepper. Coat 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 thighs for 6-7 minutes on each side until fully cooked. Let it rest for 5 minutes before slicing.
Prepare tzatziki sauce by mixing Greek yogurt, grated cucumber, minced garlic, olive oil, lemon juice, and salt until smooth.
Assemble the bowl starting with a base of cooked quinoa, then layer with sliced grilled chicken, cherry tomatoes, cucumber, and red onion.
Drizzle tzatziki sauce over the top, sprinkle with feta cheese, and garnish with fresh parsley.