Pat the chicken thighs dry with paper towels. Season both sides with kosher salt and black pepper.
Heat the olive oil in a large deep skillet or Dutch oven over medium-high heat.
Add the chicken thighs skin-side down and cook for 6-7 minutes until the skin is golden brown and crisp. Flip and cook the other side for 4 minutes. Remove chicken from the pan and set aside.
Reduce heat to medium. Add the minced garlic to the pan and sauté for 1 minute until fragrant, stirring constantly to avoid burning.
Pour in the chicken broth, scraping the bottom of the pan to loosen any browned bits.
Add the lemon slices, fresh lemon juice, dried oregano, dried thyme, and crushed red pepper flakes. Stir to combine.
Return the chicken thighs to the pan, skin-side up. Spoon some of the sauce and lemon slices over the chicken.
Cover the pan with a lid and simmer for 15 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove the lid, add the unsalted butter, and spoon the sauce over the chicken as the butter melts.
Sprinkle chopped fresh parsley over the chicken before serving.