In a large ziplock bag, dump the pesto, lemon zest and lemon juice. Seal the bag and squish it around until well combined. Add chicken to bag, seal and squish around until the chicken is coated. Place in the refrigerator and marinate for 1 to 6 hours.
Heat grill to medium high heat. Grill chicken for about 6 minutes per side or until cooked through to 165 degrees F.