Preheat a cast-iron skillet over medium heat and add 2 tablespoons of high-heat oil.
In a small bowl, combine 1 teaspoon kosher salt, 1/2 teaspoon dried oregano, 1/2 teaspoon garlic powder, and 1/4 teaspoon ground black pepper; mix and set aside.
Place aluminum foil on the counter and lay out the chicken thighs; trim any large pieces of fat if needed. Sprinkle half the seasoning over the top of the thighs.
Using tongs, place the chicken in the hot skillet seasoning-side down. Sprinkle the remaining seasoning on the underside, then cover the skillet with foil to reduce splatter.
Cook the thighs 4 minutes on the first side, then flip and cook 4 minutes on the second side.
While the chicken cooks, slice the kalamata olives into quarters, dice the roma tomatoes, and slice the lemon, removing any seeds.
After the second side is cooked, remove the foil, pour in 1/2 cup chicken stock, and scatter the olives and diced tomatoes around the chicken. Place a lemon slice on each thigh.
Bring the skillet to a brief boil, then reduce heat to low, cover, and cook 10 minutes more, or until the internal temperature reaches 165°F.
Remove from heat, garnish with parsley if desired, and serve.
