Pound each cutlet between two pieces of wax paper (or you can simply purchase thin cutlets).

In a small bowl, whisk lemon juice, zest, olive oil, mustard, garlic, thyme, rosemary, salt, pepper, and optional red pepper flakes. Place cutlets in a ziplock bag and add marinade. Put bag into a bowl to prevent leakage and place in the refrigerator overnight or for at least four hours and up to 24 hours.

Preheat grill to medium-high (or you can use a high-quality grill pan). When hot, place chicken cutlets on grill. Cook about six minutes on one side and then flip.

Begin checking the internal temperature with a meat thermometer. When the temperature reaches 165 degrees Fahrenheit (74 degrees Celsius), remove cutlets and place on a foil-lined plate. (They will continue to cook for a bit after you take them off the grill.) Cover with foil for about two minutes.

Slice and serve with any pan juices. Garnish with more thyme, rosemary, and optional parsley.