1. Rub equal amounts of lemon zest into each side of chicken breast. Sprinkle with pepper, pressing with hands to adhere.
2. Melt butter in a heavy nonstick skillet over medium heat. Sauté chicken 4 to 5 minutes per side or until golden and chicken is opaque throughout. Transfer to a platter and keep warm.
3. Add lemon juice, Worcestershire and mustard to skillet, stirring with a wooden spoon to deglaze. Serve sauce over chicken breasts and sprinkle with parsley.