Preheat the oven to 220C/425F/Gas 7.
Fry the onions in a pan with a little oil or goose fat until lightly browned.
Stir in the chickpeas and crush some of them with a fork or masher, leaving a few whole for texture.
In a bowl, combine the sausagemeat with the lemon juice and zest and the mint. Add the onions and chickpeas to the bowl and mix well by hand. Fry a little of the mixture in the pan and taste for seasoning, adding salt and pepper, to taste.
Place the goose in a large roasting tin and stuff half of the chickpea mixture into the cavity. Add the lemon shells to fill and remaining space. Roll the rest of the stuffing into balls and set aside in the fridge.
Roast the goose for 60 minutes and then reduce the temperature of the oven to 180C/350F/Gas 4.
Remove the goose from the oven and place the potatoes and the reserved stuffing balls around the bird.
Return the goose to the oven and continue cooking for 2-2½ hours, until the skin is dark brown and crisp.
Remove the goose from the oven, cover with foil and leave to rest for 15 minutes before carving. Spoon out the stuffing and roast potatoes and keep warm in the oven.
Serve with all the Christmas trimmings.