Pat the chicken thighs dry with paper towels and season both sides with kosher salt and black pepper.
Heat olive oil in a large deep skillet or Dutch oven over medium-high heat.
Add the chicken thighs skin side down and cook without moving until the skin is golden brown and crispy, about 6-7 minutes.
Flip the chicken thighs and cook the other side for 4 minutes. Remove the chicken from the skillet and set aside.
Reduce heat to medium, add the minced garlic to the skillet and sauté for 1 minute until fragrant.
Pour in the chicken broth, lemon juice, and add lemon zest, dried oregano, and crushed red pepper flakes. Stir to combine.
Return the chicken thighs to the skillet, skin side up, and spoon some sauce over the top.
Cover the skillet and simmer for 15 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove the chicken thighs and stir the unsalted butter into the sauce until melted and smooth.
Return the chicken to the skillet and spoon the sauce over the top.
Sprinkle chopped fresh parsley over the chicken before serving.