To make the Walnut Crumble, place all the ingredients except the walnuts in a bowl. Mix with your fingertips until crumbly. Add the walnuts and refrigerate until needed.
Preheat oven to 180°C (160°C fan bake).
Melt the butter in a medium pan over a medium heat. Add the sugar and mix well.
Stir in the orange juice, cinnamon and salt. Bring to a simmer.
Add the banana and toss gently until coated.
Transfer to a 25cm-diameter oven dish and top with the crumble.
Bake for 20 minutes or until the crumble is golden.
Leave to cool for 10 minutes before serving.
