In a bowl, combine all the spices together. Thoroughly brush the hens with the olive oil mixture. Twist the wings of the hens and tuck them under the body.
Make a raft of the celery ribs on the bottom of an 8 x 12 baking pan with the hens on top. Arrange the onions around the hens.
Place in the oven and reduce heat to 400°F.
Bake 55-65 minutes or just until hens reach 165°F.
Remove from the oven and loosely tent with foil for 10 minutes before cutting.
Cut hens in half and serve.
Notes
Always check for doneness using a meat thermometer to ensure the meat is thoroughly cooked. Safe poultry temperatures should reach 165°F but hens can be removed from the oven at 160°F because they will continue to cook as they rest under the foil.
For an accurate temperature reading of the hen, ensure the thermometer does not touch the bone.
Be sure to start the roasting at 450°F to initially sear the outside of the hens, locking in all the juices under the skin. Lower the heat to 400°F once the birds are in the oven.