Preheat oven to 400 degrees.
Make a paste out of olive oil, salt, pepper, paprika, garlic powder, and duck sauce.
Rub spice mixture all over the turkey. Place turkey, breast side down, in a large roasting pan. You can sprinkle on more of the pepper, paprikea, and garlic powder if desired. Let turkey come to room temperature for 20 minutes. Bake 2 hours, covered. (Tie the legs together with kitchen twine or secure with foil.).
Lower temperature to 350 degrees. and uncover. Turn turkey breast side up, being careful not to prick skin. Bake 1 hour.
Flip turkey over again and baste with pineapple juice every 15 minutes for another 1/2 to 1 hour. Turkey is done when juices run clear when pierced with a fork. Place turkey on a platter; reserve liquid in pan for gravy.
Prepare the gravy: Combine chicken stock, turkey giblets and neck if desired, quartered onion, and bay leaf in a pot. Simmer about 1 hour or until reduced to 3 cups of liquid, skimming the surface if necessary.
In a large skillet, melt margarine over medium-high heat. Add sliced onions, rosemary, and sage and saute about 15 minutes or until onions are golden. Add Potato starch; stir 1 minute. Gradually wihisk in chicken stock mixture, discarding bay leaf, turkey neck, giblets, and quartered onion. Boil about 3 minutes or until the gravy thickens, stirring often. Whisk in the vinegar.
Rewarm the gravy and thin with more chicken stock if necessary. Pour over sliced turkey or serve on the side.