Pat chicken breasts dry with paper towels. If breasts are uneven in thickness, place between plastic wrap and gently pound to an even ¾-inch thickness using a meat mallet or heavy pan.
In a glass or ceramic dish, combine olive oil, lemon juice, minced garlic, oregano, rosemary, thyme, salt, pepper, and red pepper flakes if using. Whisk thoroughly until emulsified.
Add chicken breasts to the marinade, turning to coat completely. Cover and refrigerate for at least 30 minutes or up to 4 hours.
Remove chicken from refrigerator 20 minutes before cooking to ensure even heat distribution.
Heat a large cast iron skillet over medium-high heat until a drop of water sizzles immediately when it hits the surface.
Remove chicken from marinade, allowing excess to drip off. Place chicken in hot skillet and cook undisturbed for 5-6 minutes until a golden-brown crust forms.
Turn chicken and reduce heat to medium. Cook for an additional 5-7 minutes or until internal temperature reaches 160°F (71°C) at the thickest part.
Transfer to a cutting board and tent loosely with foil. Rest for 5 minutes to allow for carryover cooking to reach 165°F (74°C) and redistribution of juices.
Slice chicken against the grain and serve with optional garnishes like fresh parsley, lemon wedges, cherry tomatoes, kalamata olives, and crumbled feta.