01 - In a medium bowl, whisk together the maple syrup, Dijon mustard, olive oil, apple cider vinegar, minced garlic, thyme, salt, and black pepper until thoroughly emulsified.
02 - Place the chicken breasts in a large resealable plastic bag or shallow dish. Pour the marinade over the meat, ensuring each piece is evenly coated. Seal the container and refrigerate for at least 1 hour, or up to 8 hours for maximum flavor infusion.
03 - Heat the grill to medium-high settings. Lightly oil the grates to prevent the chicken from sticking during the cooking process.
04 - Remove the chicken from the marinade, allowing excess liquid to drip off, and discard the used marinade. Grill the chicken for 6 to 8 minutes per side, or until the internal temperature reaches 165°F and the exterior displays golden grill marks.
05 - Transfer the grilled chicken to a platter and let it rest for 5 minutes before serving to retain juices. Garnish with additional fresh thyme if desired.