01 - In a medium mixing bowl, whisk together the maple syrup, Dijon mustard, olive oil, apple cider vinegar, minced garlic, thyme leaves, salt, and black pepper until smooth and fully combined.
02 - Place the chicken breasts in a large resealable plastic bag or shallow dish. Pour the marinade over the chicken, ensuring each piece is evenly coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 8 hours for deeper flavor penetration.
03 - Preheat your grill to medium-high heat (approximately 375–400°F). Lightly oil the grill grates to prevent the chicken from sticking.
04 - Remove the chicken from the marinade, allowing any excess to drip off. Discard the remaining marinade. Place the chicken on the preheated grill and cook for 6–8 minutes per side, depending on thickness, until the internal temperature reaches 165°F and the exterior develops golden grill marks.
05 - Transfer the grilled chicken to a cutting board and let it rest for 5 minutes to allow the juices to redistribute. Garnish with fresh thyme sprigs if desired and serve immediately.