My mum used to make this kind of bake thing with sausage meat. You put a layer of sausage meat, a layer of fried onions on top (obviously for us we'd use Frylight), then a layer of chopped tinned tomatoes, then a layer of mash. She'd bake it in the oven for about 40-45 mins. Delish!
And Joe's sausages can be bought here: Low Fat Sausages