Combine flour, baking powder, cinnamon, soda, and salt in a small bowl. Set aside.
In a large mixing bowl, beat butter and sugar till creamy, about 2 minutes. Beat in vanilla, eggs, bananas, and sour cream. Stir in dry ingredients till just combined. Don't over-mix.
Combine all topping ingredients in a small bowl and stir till well mixed.
In a well greased Bundt cake pan, layer 1/3 of the topping, then half the batter, then 1/3 of the topping and the remaining batter. Top with the last third of the topping.
Bake at 350° for 40-45 minutes or until a toothpick comes out clean.