Put the onions in the bottom of a baking dish and sit the turkey on top breast side up. Leave it to sit at room temperature for 30 minutes.
Pre-heat the oven to 185C(365F) fan-forced after 20 minutes.
Place the oil, lemon peel, garlic and rosemary in a small saucepan and heat until the lemon starts to curl at the edges.
Tuck the wing tips under the turkey.
Fill the bottom cavity loosely with stuffing then stuff the neck cavity and cover them both with skin.
Tie the legs together with kitchen twine.
Baste the bird.
Bake it for 30-45 minutes or until golden, basting after 30 minutes and then reduce the temperature to 150C(302F) and bake for another 3 hours, basting every 30 minutes.
Take the turkey out of the oven and cover it with foil then leave it to rest for 30 minutes.
Carve it and serve it up.