Dice the onion. Chop the walnuts and cranberries in half.
Combine all the ingredients in a large mixing bowl, getting your hands in to give it a good mix.
Add the mixture to an ovenproof dish and cover with greaseproof paper or tin foil.
Bake in the oven for 30 minutes. Remove the greaseproof paper/foil and mix, breaking up your stuffing into little chunks with a spoon. Put back in the oven for a further 10 minutes (uncovered) to crisp up the edges.