In a medium bowl, whisk the olive oil with the zest and juice of one orange, ½ teaspoon salt, ¼ teaspoon black pepper, garlic, chili powder and paprika. Place chicken and orange slices in the marinade and toss well to combine. Let rest in the refrigerator for at least one hour--ideally, overnight.
Preheat oven to 375 degrees. Remove the chicken from the marinade and sprinkle with parsley. Heat a large skillet over medium-high heat. Once the skillet is hot, reduce to medium and place the chicken in the pan, skin side down. Sear until it is golden brown, about 5 to 7 minutes. Turn the thighs over and place the pan in the oven to finish roasting, about 20-25 minutes, or until the juices run clear or a thermometer reads 145-150 degrees. Pull the chicken out of the oven and let rest for five minutes before serving.