If your bananas are not ripe/blackened, place them on a baking tray and bake at 180C/350F for 25-30 minutes. Leave to cool then mash.
In a bowl, combine the mashed bananas, eggs, butter, oil and sugar. Mix well.
Into the banana mixture, add flour, baking powder, baking soda, cinnamon, pinch of salt and walnuts. Fold until just combined.
Pour and level mixture into a lined baking pan. Top with 2 banana halves and sprinkle over with some raw sugar. Bake at 180C / 350F for 55-60 minutes or until when toothpick comes with minimal crumbs attached. If the toothpick is clean, it's overbaked.