Step 1: Prepare the Chicken - Place the boneless chicken breasts on a cutting board and gently pound them with a meat mallet or rolling pin until they are evenly flat.
Step 2: Make the Marinade - In a small blender or mixer jar, combine the extra virgin olive oil, fresh lemon juice, chili flakes, dried oregano, garlic cloves, brown sugar, whole grain mustard, black pepper, and salt. Blend until smooth and well combined. Add the fresh parsley leaves and pulse briefly to fold in the herbs.
Step 3: Marinate the Chicken - Transfer the flattened chicken breasts to a large bowl and pour the prepared marinade evenly over each piece. Cover the bowl and refrigerate for at least 30 minutes.
Step 4: Grill the Chicken - Heat a grill pan over medium heat until fully hot. Place the marinated chicken breasts directly onto the pan. Cook for about 4 minutes on the first side, then flip and cook for another 3 to 4 minutes.
Step 5: Rest and Serve - Remove the chicken from the grill pan and transfer to a clean plate. Allow it to rest for 5 minutes before slicing or serving.
