Pound chicken breasts on a work surface to at least 1/2-inch thickness.
Whisk safflower oil, lemon juice, garlic, and Italian seasoning together in a bowl and pour into a resealable plastic bag. Add chicken, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 6 to 24 hours.
Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Remove chicken from the marinade and shake off excess. Discard the remaining marinade.
Cook chicken on preheated grill until longer pink in the center, about 3 minutes per side. Transfer chicken to a plate and let sit for 10 minutes before serving.
