Arrange a rack in the middle of the oven and heat the oven to 400°F.
Bring a medium pot of salted water to a boil.
Quarter 1 ½ pounds small Yukon gold potatoes.
Thinly slice half of 1 medium lemon and remove the seeds from the slices; reserve the remaining half.
Thinly slice 3 garlic cloves.
Pat 4 bone-in, skin-on chicken thighs dry with paper towels and season with ½ teaspoon of the kosher salt and ¼ teaspoon of the black pepper.
Drizzle 1 tablespoon olive oil into a 10-inch or larger oven-safe skillet.
Add the chicken, skin-side down. Cook undisturbed over medium heat until the skin is well-browned and crisp, about 15 minutes.
Meanwhile, add the potatoes to the boiling water and cook until fork tender, about 10 minutes, then drain.
Transfer the chicken to a plate, skin-side up.
Add the potatoes, garlic, 2 teaspoons dried oregano, remaining ½ teaspoon kosher salt, and remaining ¼ teaspoon black pepper to the skillet.
Cook, stirring occasionally, until the potatoes are lightly browned in spots, 3 to 5 minutes.
Nestle the chicken on top of the potatoes and top with the lemon slices.
Roast in the oven until the chicken is cooked through, 8 to 10 minutes.
Squeeze the juice from the reserved lemon half over the chicken and potatoes.
Garnish with chopped fresh parsley, if desired.
