To make the marinade, in a small bowl or jar, whisk together balsamic vinegar, olive oil, maple syrup, Dijon mustard, garlic, fresh thyme, salt, pepper and pinch of cayenne pepper until all combined.

Place the chicken breasts in a shallow dish or a 1-gallon sealable plastic bag and add most of the marinade (I recommend reserving a little bit of the marinade to brush on the chicken later while grilling)

Place the chicken in the fridge and let it marinate for at least 1 hour or up to 12 hours.  When ready to grill, remove the chicken from the dish or bag, shake off any excess and discard the leftover marinade.

Heat a grill or grill pan on medium heat and brush the grill with oil to prevent the chicken from sticking.  Grill the chicken 5 to 6 minutes on each side, or until cooked through and no longer pink (chicken should have an internal temp of 165 degrees).

Remove the chicken from the grill and let it rest for 5 minutes before serving.  Enjoy!