Prepare the marinade by whisking the olive oil, Dijon mustard, garlic, salt and pepper in a large bowl.
Add the chicken breast into the bowl and toss to combine and evenly coat the chicken with the marinade. Refrigerate and let marinate for 2 hours or up to 24 hours.
Preheat grill or grill pan to medium heat. Place chicken on the grill for 5-7 minutes. Flip over and cook until golden brown and the juices run dry, approximately 5-7 more minutes.
Remove chicken from the grill. Sprinkle with parsley and serve as desired.
Video
Notes
Storage: Store any leftovers in an airtight container. They will last up to 4 days.