Combine first 5 ingredients, 1/4 teaspoon salt, and garlic in a bowl.
Remove giblets and necks from hens. Rinse hens in cold water; pat dry. Split hens into halves; trim excess fat. Loosen skin from breasts and drumsticks by inserting fingers and gently pushing between skin and meat. Rub equal parts of spice mixture under loosened skin. Sprinkle hens with 1/4 teaspoon salt and pepper.
Place chicken on grill rack coated with cooking spray; grill 10 minutes on each side or until juices run clear. Remove and discard skin.