Preheat a cast iron skillet over medium heat and add 2 tablespoons of a high heat oil (like avocado or canola).
In a small dish, measure out the kosher salt, dried oregano, garlic powder, and ground black pepper. Mix it together until well combined then set aside.
Place a medium-to-large piece of aluminum foil on the counter and lay the chicken thighs out on top of it. If necessary, use a sharp knife to carefully cut away any large pieces of fat on the thighs.
Sprinkle half of the seasoning mixture onto the tops of the chicken thighs, then use a pair of tongs to place them (seasoning side down) in the heated skillet. Sprinkle the remaining seasoning on the back sides of the thighs, then cover the skillet with the aluminum foil to reduce splatter.
Cook the thighs for 4 minutes on one side, then flip them over with the tongs and cook for 4 minutes on the other side. While the chicken is cooking, use a knife and cutting board to slice the kalamata olives into fourths, dice the tomatoes, and slice the lemon (removing any seeds).
Once the chicken thighs have finished cooking on the second side, remove the foil, pour in the chicken stock, and spread the olives and diced tomatoes into the pan around the chicken. Place a slice of lemon on top of each chicken thigh, then bring the mixture to a boil (this will not take long). Turn the heat to low, then cover and cook for 10 minutes. The thighs will be done once the internal temperature has reached 165 degrees F. once done, garnish with parsley (if desired), then serve!