Preheat your oven to 425 degrees F.
Combine garlic powder, salt and pepper in a small bowl.
Pat skin side of chicken dry with paper towels.
Season chicken with garlic powder mixture on both sides.
Heat olive oil over medium high heat in a large cast iron or oven-proof skillet. Place chicken skin-side down and sear until golden brown, approximately 2 to 3 minutes per side. Use a splatter screen if you have one.
Carefully remove from heat (be sure to use an oven mitt) and allow the grease to settle for about a minute. Sprinkle evenly with rosemary and lemon zest.
Carefully transfer to preheated oven and bake for 25 minutes, or until chicken is no longer pink, juices run clear and internal temperature is 165 degrees F (bake time will depend upon size of thighs).
Allow chicken to rest for about 5 minutes before serving.
Garnish with fresh rosemary sprigs and/or lemon slices, if desired.