Pat the chicken thighs dry with paper towels. Season both sides with 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 for 5-7 minutes until the skin is golden brown and crispy. Flip and cook the other side for 3-4 minutes. Remove chicken from the pan and set aside.
Reduce heat to medium. Add minced garlic to the pan and sauté for 1 minute until fragrant, stirring constantly to avoid burning.
Pour in the chicken broth, lemon juice, and add lemon zest, dried oregano, and crushed red pepper flakes. Stir to combine and scrape up any browned bits from the bottom of the pan.
Return the chicken thighs to the pan, skin side up. Cover and simmer for 15-18 minutes until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove the chicken thighs and set aside on a plate. Increase heat to medium-high and cook the sauce for 3-4 minutes to reduce slightly.
Stir in the unsalted butter until melted and the sauce is glossy.
Return the chicken to the pan and spoon the sauce over the top.
Sprinkle chopped fresh parsley over the chicken before serving.