In a bowl, mix together olive oil, dried oregano, garlic powder, onion powder, smoked paprika, salt, and pepper. Add the chicken thighs and coat well. Cover and marinate for at least 30 minutes (or up to overnight in the refrigerator if time permits).
Preheat a grill or stovetop skillet over medium-high heat. Remove chicken from the marinade and grill for about 6-7 minutes on each side or until fully cooked and the internal temperature reaches 165°F (75°C). Remove from heat and let rest for a few minutes before slicing.
In a small bowl, combine Greek yogurt, minced garlic, lemon juice, dried dill, and a pinch of salt. Mix until well combined and set aside.
In serving bowls, layer cooked quinoa (or rice) as the base. Top with sliced grilled chicken, halved cherry tomatoes, diced cucumber, and sliced red onion.
Drizzle a generous amount of tzatziki sauce over the assembled ingredients and garnish with freshly chopped parsley.
Warm up pita bread and serve alongside the bowls for a complete meal.