Preheat the oven to 200°C/180°C fan/gas mark 6.
Blitz the bread in a food processor until it resembles fine breadcrumbs.
In a pan fry the onions in the butter until golden brown, then add the sage, ProZero and breadcrumbs.
Fry for further 1 minute and then place into a greased baking dish and bake in the oven for 20 minutes.
Fate Low Protein All-Purpose Mix and ProZero are foods for special medical purposes and must be used under medical supervision.