Remove and discard giblets and necks from hens. Rinse hens under cold water; pat dry. Remove skin; trim excess fat. Split hens in half lengthwise. Sprinkle salt and ½ teaspoon pepper over hen halves; set aside.
Combine mustard and next 5 ingredients in a small bowl; set aside.
Prepare the grill or broiler. Place hen halves, meaty sides up, on grill rack or rack of a broiler pan coated with cooking spray; cook 15 minutes on each side or until juices run clear, basting occasionally with mustard mixture.
Notes
If you are preparing this recipe as gluten-free, just be sure to use a brand of mustard that is known to be GF.