Place the raw chicken boneless skinless breasts on top of a cutting board and cover them with a piece of plastic wrap - this helps keep any juices from splattering.
Use a meat mallet or rolling pin to pound on the thicker portion of each chicken breast. You want forceful blows that can help thin the chicken out. Once each breast is about the same thickness (roughly one-third to one-half an inch), you can stop.
Measure out marinade ingredients and place them into a measuring cup or medium bowl. Use a small whisk to mix until thoroughly combined. Set aside.
Place the flattened raw chicken breasts in a sealable plastic bag. Pour in about 2 ounces of marinade, leave the remaining ounce in the cup or bowl. Press air as best you can out of the plastic bag, then seal it. Squish everything together in the bag to help cover the chicken with the marinade, then place the marinating chicken in the fridge for 15 minutes.
After the 15 minutes are up, remove the bag with the chicken breasts from the fridge and place it on the counter to warm slightly for 15 minutes. While the chicken is warming on the counter, turn your grill on to a medium heat and let it get to a temperature of around 375 to 400 degrees F.
Once the second 15 minutes are up and the grill is up to temperature, use a pair of tongs to remove each chicken breasts from the bag and place on the grill - you can throw the leftover marinade and bag away.
Let the breasts cook for 5 minutes with the grill lid closed, then use the tongs to flip the chicken breast so the other side is on the grill grates. Close the grill lid and let the breasts cook another 3 to 5 minutes, until the internal temperature is roughly 135 to 145 degrees F.
Open the grill lid again and use a basting brush to coat a layer of the reserved marinade onto each chicken breast. Close the lid again and let the breasts cook until they reach an internal temperature of 165 degrees F in the thickest part of the breast, anywhere from 3 to 7 minutes depending on how thick your chicken breasts are. Then remove from the grill, let rest 5 to 10 minutes, and serve! You can also brush on a little additional of the reserved marinade if desired.