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 smooth and well combined.
02 - Place the chicken breasts in a large resealable bag or shallow dish. Pour the marinade over the chicken, ensuring all pieces are evenly coated. Seal or cover tightly and refrigerate for at least 1 hour, or up to 8 hours for a more pronounced flavor.
03 - Preheat your grill to medium-high heat. Lightly oil the grill grates to prevent sticking.
04 - Remove the chicken from the marinade, shaking off any excess. Discard the remaining marinade. Grill the chicken for 5 to 7 minutes per side, or until fully cooked through and the internal temperature reaches 165°F (74°C).
05 - Transfer the chicken from the grill to a cutting board and let it rest for 5 minutes before slicing. Garnish with fresh parsley and serve alongside lemon wedges if desired.