Whisk together the olive oil, balsalmic vinegar, garlic, Italian seasoning, salt, and pepper.
Pound the chicken breast using a meat tenderizer.
Place the chicken breast and marinade in a ziploc bag. Squish it around to coat the chicken.
Place the bag in the fridge for 1 hour (this is flexible, anywhere from 10 min to 3 hours is okay).
Grill over medium high heat for 8-10 minutes per side, until no longer pink inside or the internal temperature reads 160 degrees.