01 - In a medium bowl, whisk together the maple syrup, Dijon mustard, olive oil, apple cider vinegar, garlic, thyme, salt, and black pepper until thoroughly combined and smooth.
02 - Place the chicken breasts in a large resealable bag or shallow dish. Pour the marinade over the chicken, making sure every piece is evenly coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 8 hours for 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, and discard the leftover marinade. Grill the chicken for 5 to 7 minutes per side, until fully cooked through and the internal temperature reaches 165°F.
05 - Transfer the chicken off the grill and let it rest for 5 minutes before slicing. Garnish with fresh parsley and serve with lemon wedges alongside grilled vegetables or a crisp green salad.