Stir together flour, 1 1/3 cups oats, salt and bicarb soda.
In a large bowl, cream 125g butter or margarine with 2/3 cup (110g) brown sugar. Beat in the eggs, then the bananas and vanilla. Beat the flour mixture into the banana mixture. Pour the batter into a greased and floured 20cm square tin.
Mix 3/4 cup oats, 1/3 cup (50g) brown sugar, 40g melted butter or margarine, walnuts and cinnamon together until crumbly. Sprinkle evenly over the top of the batter.
Bake in preheated oven at 180 degrees C for 40 to 45 minutes, or until it tests done. Transfer to a rack to cool.
The is the most awesome recipe. I make this cake all the time. Who knew that adding SO much oats would work. I did not. Higher in fibre thanks to all the oats too, compared to your regular cake recipe. Also works a treat with macadamias instead of walnuts. - 20 Aug 2013