Flatten the Chicken - Thoroughly dry the chicken with paper towels. Cut each piece horizontally lengthwise to make two thinner cutlets, four total. Place one of the pieces between two plastic sheets or in a large plastic bag and flatten with a meat tenderizer to an even ¼-inch thickness. Repeat with the remaining pieces. Generously season both sides with salt and pepper.
Set up the Breading Station - In one shallow bowl, mix the flour, 1 teaspoon kosher salt, and ½ teaspoon black pepper. In a second shallow bowl, whisk together eggs, mustard, and olive oil. In a third shallow bowl, combine the panko breadcrumbs with lemon zest (if using).
Bread the Chicken - Dip the chicken in flour, shaking off any excess coating. Next, dip in the egg mixture, coat completely and drain any excess. Lastly, dip in the breadcrumbs, pressing to coat evenly. Repeat the process with the remaining pieces.
Pan-fry the Chicken - Heat ⅓ cup of vegetable oil in a 12-inch nonstick skillet over medium heat. Once the oil is shimmering, about 350ºF (177ºC), carefully place two chicken pieces in the pan. Fry until the first side is golden brown and crispy, about 2 to 3 minutes. Cook until an internal temperature of 160 to 165ºF (71 to 74ºC) on a meat thermometer, about 2 to 4 minutes.Transfer to a paper towel-lined plate to briefly drain the excess oil for 15 seconds. Place on a wire rack set on top of a sheet pan. Discard the extra oil and wipe the pan clean. Add ⅓ cup of fresh vegetable oil, and repeat the same cooking procedure with the two remaining pieces.
To Serve - Garnish with parsley and lemon wedges.
Notes
Storing: Store in an airtight container for up to 5 days.
Reheating: Reheat individual pieces in the microwave on high power in 15 to 30-second intervals until hot. Alternatively, place on a foil-lined sheet pan and bake at 375ºF (191ºC) until hot and crispy, about 10 to 15 minutes.
Using Smaller Pieces: Four chicken breasts, about 6 to 8 ounces, can be used. Flatten until ¼-inch thick.
Bread crumbs: Traditional fine breadcrumbs can be used but won’t be as crunchy.
Make-Ahead: The chicken can be breaded, covered, and refrigerated for 1 day before cooking.
Baking: Bake chicken in the middle of the oven at 450ºF (232ºC) on top of a wire rack set on a foil-lined sheet pan until the internal temperature reaches between 160 to 165ºF (71 to 74ºC), about 15 to 20 minutes.
Make it Gluten-Free: Use gluten-free flour and breadcrumbs.