Combine in a medium bowl and whisk together:
¼ cup Dijon mustard
¼ cup balsamic vinegar
¼ cup fresh lemon juice
4 large cloves garlic, minced
1 T. minced fresh rosemary
½ tsp. pepper
¼-½ cup olive oil
Wash and pat dry:
4 chicken breasts, skinned and boned
Place chicken and marinade in a ziplock bag and marinade at room temperature for 2 hours or in refrigerator 4-6 hours or overnight.
Grill chicken for 5-6 minutes per side or until it springs to the touch.