To make the marinade: in a medium bowl, whisk together the garlic infused oil, lemon juice, lemon zest, oregano, salt, and pepper.
Butterfly the chicken breasts (I usually cut completely through to create 4 thin fillets). Place each piece into a large resealable plastic bag one at a time, lying flat and pounding to an even thickness.
Place all the chicken breasts in the plastic bag and pour the marinade over top. Shake gently to coat the chicken. Squeeze air out of bag and seal. Marinate in the refrigerator at least 30 minutes, or up to 2 hours.
Lightly oil grill and heat to medium-high heat (about 350 to 400 degrees F). Grill chicken breasts until golden brown, about 8 to 10 minutes, flipping half-way through, until chicken has reached an internal temperature of 165 degrees F. Serve.
Notes
Note: You can also make homemade garlic-infused oil but be sure to cool the oil completely before using in the marinade.