Remove the wing tips of each hen with a pair of poultry shears. Cut along each side of the backbone and remove it. Place a hen breast side up on a cutting board. Flatten hen with the palm of your hand to break the breastbone and collapse the hen. Make a small incision between each leg and bottom end of the breastbone and pass through the ends of legs to hold them in place. Thread 1 (8-inch) skewer through the wings of each hen and another through the legs to hold the birds flat. Repeat with remaining hen. Place hens in a shallow container. Pour over the marinade, and sprinkle with cilantro. Marinate the hens at least 6 hours or overnight. Prepare a charcoal or gas grill, arranging coals for indirect cooking. The coals should be moderately hot. Remove the hens from the marinade; discard marinade. Grill until the juices run clear when pierced with a fork and an instant read thermometer registers 180 degrees F when inserted into the thickest part, 15 to 20 minutes per side.
Combine all ingredients, and place in a clean 2-quart jar. Store covered in the refrigerator for up to 2 weeks. Shake well before using. This marinade works well with seafood, poultry, or steamed vegetables. Yield: 1 1/2 quarts