Preheat the oven to 400°F (200°C). Place a rack in the middle of the oven.
Pat the chicken thighs dry with paper towels. Drizzle the chicken with olive oil, rub to coat, and season with salt and pepper.
In a large cast iron or other heavy bottomed oven-safe skillet, place the chicken skin-side down. Scatter the olives around the thighs. Place the skillet over medium heat and cook, undisturbed, until the skin is well browned and crisp, 12 to 20 minutes.
While the chicken is cooking, slice half the lemon into thin rounds. Remove the seeds from the lemon slices.
Flip the chicken and scatter the lemon slices around it. Transfer the skillet to the oven. Roast until the chicken is cooked through and registers an internal temperature of 165°F (74°C), 8 to 15 minutes more.
Squeeze the remaining lemon half over the chicken, sprinkle with parsley, if desired, and serve.