Place chicken breasts, single layer, into an ungreased 13x9-inch baking dish or a resealable plastic bag.
In a large bowl, combine balsamic vinegar, whole grain mustard, Dijon mustard, garlic, lime juice, brown sugar, olive oil, and pepper. Pour marinade over chicken breasts. Cover and refrigerate for at least 8 hours (turning meat over several times).
Preheat Barbecue grill (spray grill with vegetable-oil cooking spray). Place chicken onto hot grill and brush with remaining Balsamic-Dijon marinade. Cover barbecue with lid, open any vents, and cook 20 to 30 minutes or until a meat thermometer registers an internal temperature of 165 degrees F. (juices will run clear when cut with the tip of a knife); turning and basting several times.
Remove from chicken from the grill, transfer onto a serving platter, and serve immediately.
Makes 4 servings.
* The U.S. Department of Agriculture, as well as food agencies in the United Kingdom and elsewhere, advises against washing poultry. Rinsing chicken will not remove or kill much bacteria, and the splashing of water around the sink can spread the bacteria found in raw chicken. Cooking poultry to 165 degrees Fahrenheit effectively destroys the most common culprits behind food-borne illness.
Grilled Balsamic-Dijon Chicken Recipe: https://whatscookingamerica.net/poultry/balsamicdijonchicken.htm