Place the chicken breasts between two sheets of plastic wrap and gently pound to an even thickness (about 1/2–3/4 inch) so they cook evenly. Put the chicken in a shallow dish or resealable bag and pour the marinade over it, turning to coat. Marinate at room temperature for 15–30 minutes or refrigerate for up to 2 hours. If refrigerated, let sit 15 minutes at room temperature before cooking.

Cook chicken

Heat a large skillet (preferably heavy-bottomed or cast-iron) over medium-high heat until hot. Add 1 tbs olive oil to the pan and swirl to coat. Remove chicken from marinade, letting excess drip off. Place breasts in the skillet without overcrowding. Cook undisturbed for 4–5 minutes until a golden crust forms, then flip and reduce heat to medium. Cook another 4–5 minutes until the internal temperature reaches 165°F (74°C) or juices run clear. Transfer chicken to a plate and tent loosely with foil to rest for 5 minutes.

Pan sauce (optional)

Make pan sauce

With the skillet still over medium heat, add the chicken stock and use a wooden spoon to scrape up browned bits from the bottom of the pan. Let the stock reduce for 1–2 minutes. Stir in the butter and lemon zest, swirling until the butter melts and the sauce is glossy.

Finish and serve

Return the rested chicken to the skillet briefly to warm and coat with sauce, or slice the chicken and spoon sauce over the top. Sprinkle with chopped parsley and serve immediately.