Stuff the turkey cavity with the halved orange, onion, and rosemary sprigs. Tuck the wing tips behind the turkey’s back and tie the legs together with twine. Rub oil evenly over the turkey and season lightly with salt and pepper.
Place the turkey in a roasting pan and cover with aluminum foil. Cook until a thermometer inserted into the thickest part of the thigh reads 155°F (avoid touching the bone), about 2–2½ hours. Let rest 30 minutes before carving.
Carve the turkey and garnish with fresh herbs and kumquats.
