In a gallon-sized ziptop bag, combine all of the marinade ingredients, swishing them around to mix well.
If the chicken breasts you're using total 1.25lbs, they will likely be under 1" thick, which is perfect. If yours are not, or if you're using larger breast pieces, pound them with a rolling pin or meat mallet to under 1" thickness.
Place the chicken breasts in the marinade bag, squeezing all the excess air out. Toss them around in the bag to coat in the marinade, then let sit at room temperature for one hour***. Make sure they are resting on the counter in a single layer, without the breasts on top of each other.
Preheat all 3 burners of a gas grill over high heat for at least 10 minutes, which should get the internal temperature to at least 600F (once you open the lid and start cooking, it will likely hover around 400F, which is perfect).
Add the chicken breasts to the grill, close the lid, and let cook for 2 minutes.
Open the lid, and turn the meat 90 degrees, cooking on the same side for another 2 minutes. This creates grill marks and caramelization going the other way.
Flip the chicken over, and repeat on the other side, cooking for 2 minutes with the lid closed, then turning 90 degrees, and cooking for 2 more minutes, lid closed.
Check the internal temperature of the breasts using a thermometer. It's done when it's 160F or above, as it will rise about 5 more degrees from carryover cooking. If the chicken is not 160F, flip the pieces over again (to the first side) and cook for another 2 minutes, lid closed, and check again.
Let the meat rest for 5 minutes before slicing and serving. Enjoy!
*The marinade is flexible to substitutions:
Lemon juice – Try an equal amount of lime juice.
Thyme – You can substitute dried oregano, rosemary, basil, or parsley here, or even do a mix. I like to use dried herbs for convenience, but you can also use fresh. Just double the amount used.
Olive Oil – You can also use avocado oil here if you prefer.
Dijon mustard – If you’re not a fan of mustard, feel free to swap in soy sauce, coconut aminos, balsamic vinegar, or a half amount of Worcestershire sauce.
**I use equal amounts of lemon and oil here, which helps flavor and tenderize the chicken in a short amount of time. The chicken is fairly lemony, but I love it. If you tend to like less of a tangy flavor, cut the amount of lemon juice in half, to 1 tbsp.***You can get away with marinating for only 30 minutes, but an hour is better. If you want to marinate for a day, cut the amount of lemon juice in half, to 1 tbsp.Storage: Keep leftover chicken breast in an airtight container in the fridge for up to 5 days, or in the freezer for up to 2 months.Reheating: Microwave at 70% power for about 60 seconds per chicken breast. Timing will vary.