Preheat your grill or a grill pan over medium-high heat.
In a bowl, combine olive oil, oregano, garlic powder, onion powder, paprika, salt, and pepper. Add the chicken thighs and coat them well with the marinade. Let it sit for at least 15 minutes.
Grill the chicken for 6-7 minutes on each side or until fully cooked and juices run clear. Remove from the grill and let it rest for 5 minutes before slicing.
In serving bowls, layer the cooked quinoa, sliced grilled chicken, cherry tomatoes, cucumber, red onion, and feta cheese.
Drizzle tzatziki sauce over the top and sprinkle with fresh parsley. Serve immediately.