1. Heat oven to 350 degrees F. Coat 13 x 9 x 2-inch baking pan with cooking spray.Crunch Topping:
2. In bowl, combine flour and sugar. With pastry blender, cut in butter until mixture resembles fine crumbs. Stir in pecans. Set aside.Cake:
3. In large bowl, mix flour, cinnamon, salt, and baking soda. In large bowl, beat together on medium speed, sugar, mashed banana, oil, eggs, buttermilk, and vanilla until blended, 1 to 2 minutes. On low speed, gradually add flour mixture until blended. Stir in pecans. Pour into prepared pan. Crumble Crunch Topping evenly over top.
4. Bake at 350 degrees F for 50 to 55 minutes, until wooden pick tests clean. Let cake cool in pan on rack. To serve, sprinkle with sugar, if desired. Refrigerate, covered, up to 3 days.