Pat chicken thighs dry with paper towels. In a small bowl, combine oregano, garlic powder, paprika, salt, and pepper. Season chicken evenly on both sides with the spice mixture.
Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add chicken thighs and cook for 6-7 minutes until golden brown. Flip and cook another 6-8 minutes until internal temperature reaches 165°F. Remove from heat and let rest 5 minutes, then slice.
While chicken cooks, make tzatziki by combining Greek yogurt, minced garlic, dill, lemon juice, and salt in a small bowl. Mix well and set aside.
Prepare vegetables by halving cherry tomatoes, dicing cucumber, and halving olives if needed.
To assemble bowls, divide cooked rice or quinoa among 4 bowls. Top each with sliced chicken, tomatoes, cucumber, olives, and crumbled feta.
Drizzle tzatziki over each bowl and serve immediately. Store any leftover components separately in the refrigerator.
Notes
Storage tip: Cooked chicken keeps in fridge for up to 4 days. Reheat gently in a skillet with a splash of broth. Tzatziki can be made 2-3 days ahead and improves in flavor as it sits.