Remove the paper-like outer skin from the garlic heads, and separate the cloves. Do not peel the cloves. Set them aside.
Cut the onion in half, and then in slivers. Set it aside.
Rinse the chicken well and pat it dry. Set the giblets aside. Sprinkle the cavity with the tarragon and salt and pepper. Place the lemons and the rosemary sprigs in the cavit