Combine the olive oil, cumin, coriander, cinnamon, ground fennel and paprika in a small bowl. Pat the capon dry with paper towels and place on a baking sheet. Rub the spiced oil all over the skin and inside the cavity. Season inside and out with salt and pepper. Stuff the garlic and lemons inside the cavity. Cover with plastic wrap and refrigerate overnight.
Remove the capon from the refrigerator and uncover about 30 minutes before roasting. Whisk the pomegranate molasses and mustard in a small bowl; set aside. Position a rack in the lower third of the oven and preheat to 450 degrees F. Set a rack in a large roasting pan and brush with olive oil; add the chicken broth and onion to the pan. Put the capon on the rack breast-side down. Roast until the skin starts to brown and crisp, about 30 minutes.
Remove the capon from the oven and reduce the oven temperature to 375 degrees F. Insert a wooden spoon into the cavity of the capon and carefully turn it breast-side up. Baste with the pan drippings. Continue roasting, basting every 30 minutes, until the skin is browned and a thermometer inserted into the thigh registers 165 degrees F, about 1 1/2 hours to 1 hour 45 minutes. Brush with half of the pomegranate glaze during the last 15 minutes of roasting.
Transfer the capon to a cutting board and brush with the remaining pomegranate glaze. Let rest 20 minutes before carving.
Strain the pan juices into a fat separator. Pour the liquid into a gravy boat or small bowl, leaving any fat in the cup. (Alternatively, strain the pan juices into a glass measuring cup and skim off the fat with a spoon.) Carve the capon and serve with the pan juices.
A capon is a chicken that¿s larger than an average roaster; great for a crowd. You can also use a small turkey for this recipe.