Preheat oven to 175 C. Cover with baking paper rectangular tray sizes 33h23sm, the paper cover and sides of the pan. Prepare crumbs - Confusion flour and brown sugar, add the butter , confusion with hands mixture and rub with fingertips until get crumbs. Add the walnuts. Mix the banana puree, the oil, sugar, eggs, yogurt, cinnamon and salt and stir with a spoon until a uniform mixture. Add flour and baking soda and stir until flour is taken. Pour mixture evenly in baking dish covered with paper. Sprinkle top with crumbs. Bake about 40 minutes or until stuck in the middle of a toothpick comes out clean. Allow to cool. Grasp the edges of the paper and remove the cake from the pan. Cut it in 20 pieces.