Zest and juice one lemon into a large bowl. Add olive oil, garlic, Italian seasoning, red pepper flakes, and parsley. Whisk to combine and set aside.
Slice chicken breasts horizontally into thin cutlets. If necessary, cover with plastic wrap and pound with a kitchen mallet to flatten.
Pat chicken dry with paper towels and season both sides with salt and pepper. Submerge chicken in the marinade, cover, and refrigerate for 30 minutes to 2 hours.
Heat 2 tablespoons of olive oil in a large cast iron skillet over medium heat. Sear chicken in batches for 4 minutes per side until golden brown and juices run clear.
Remove chicken from heat at 160°F, tent with foil, and rest for 5 minutes until it reaches 165°F. Slice the remaining lemon while the chicken rests.
Garnish the chicken with chopped parsley and lemon slices, then serve.
