In a medium size bowl, whisk together honey, mustards, olive oil, vinegar, and garlic. Set aside.
If needed, cut chicken breasts into smaller pieces; place in a large zip-top bag. Pour half of marinade over chicken breasts. Knead to combine and refrigerate at least 2 hours.
Preheat grill to medium-heat. Using tongs, place chicken breasts on the grill. Cover and cook for 5 - 7 minutes. Turn breasts over and grill for 5 - 7 minutes longer or until a thermometer reads 165 degrees Fahrenheit.
NOTE: Reserve remaining marinade and half of grilled chicken for the honey mustard chicken tossed salad recipe (Week 9 of Summer Meals!)