Preheat the oven to 220°C.
Fry the chopped onions in goose fat or oil until lightly browned.
Stir in the chickpeas and crush some of them with a masher.
Combine sausagemeat, lemon zest, lemon juice, mint, onions, and chickpeas in a bowl.
Season the mixture with salt and pepper after tasting a small fried sample.
Stuff half the mixture and the lemon shells into the goose cavity.
Roll the remaining stuffing into balls and chill in the fridge.
Roast the goose for 60 minutes at 220°C then reduce to 180°C.
Place the potatoes and stuffing balls around the bird in the roasting tin.
Cook for a further 2 to 2.5 hours until the skin is crisp and brown.
Rest the goose under foil for 15 minutes before carving and serving.