01 - In a medium mixing bowl, whisk together the maple syrup, Dijon mustard, olive oil, apple cider vinegar, minced garlic, thyme, salt, and pepper until smooth and well combined. If desired, set aside 2 tablespoons of the marinade for basting before adding raw chicken.
02 - Place the chicken breasts in a large resealable plastic bag or a shallow dish. Pour the marinade over the chicken, ensuring each piece is thoroughly coated. Seal the bag or cover the dish and refrigerate for at least 1 hour and up to 8 hours for deeper flavor penetration.
03 - Preheat an outdoor grill or grill pan to medium-high heat (approximately 375°F to 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 used marinade. Place the chicken on the hot grill and cook for 6 to 8 minutes per side, depending on thickness, until the internal temperature reaches 165°F and the exterior develops golden grill marks. If reserved, brush with extra marinade during the final minute of cooking.
05 - Transfer the grilled chicken to a cutting board and let it rest for 5 minutes to allow the juices to redistribute. Slice and garnish with fresh thyme sprigs if desired. Serve alongside grilled vegetables or a crisp green salad.