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 the mixture is smooth and fully emulsified.
02 - Place the chicken breasts in a large resealable plastic bag or a shallow dish. Pour the marinade over the meat, turning to coat all sides. Seal or cover and refrigerate for at least 1 hour, or up to 8 hours for enhanced flavor.
03 - Prepare your grill for medium-high heat. Lightly oil the grill grates to prevent sticking.
04 - Remove the chicken from the marinade, allowing excess liquid to drip off. Discard the used marinade. Grill the chicken for 5 to 7 minutes per side, or until the internal temperature reaches 165°F.
05 - Transfer the cooked chicken to a clean plate and let it rest for 5 minutes to redistribute the juices. Garnish with chopped parsley and lemon wedges if desired.