01 - In a medium bowl, whisk together the maple syrup, Dijon mustard, olive oil, apple cider vinegar, minced garlic, thyme, salt, and pepper until smooth and well 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 thoroughly coated. Seal or cover and refrigerate for at least 1 hour, or up to 8 hours for deeper flavor penetration.
03 - Preheat grill to medium-high heat (approximately 375°F to 400°F). Lightly oil the grill grates to prevent sticking.
04 - Remove the chicken from the marinade, allowing excess to drip off. Discard any remaining marinade. Grill the chicken for 6 to 8 minutes per side, depending on thickness, until the internal temperature reaches 165°F and golden grill marks form.
05 - Transfer the grilled chicken to a plate or cutting board and let rest for 5 minutes before slicing. Garnish with fresh thyme sprigs if desired. Serve alongside grilled vegetables or a crisp salad.