Preheat oven to 350 degrees F. Spray a 9x13 or 8x11 glass pan with nonstick spray.
In a large bowl, combine the eggs, sugar, melted butter, buttermilk and vanilla. Stir until combined. Add in bananas.
Combine dry ingredients in a separate bowl. Mix 1/3 of the dry ingredients into the wet ingredients, stirring just until combined. Repeat until ingredients are completely mixed. (Note: quick breads/ cakes like this do better if mixed by hand! Don't over mix and it's okay if there are a few lumps!)
Pour batter in the prepared pan.
To prepare the crumb topping, combine all ingredients except butter. Cut butter into small pieces and add to the mixture. Using a pastry cutter (or 2 forks) blend the ingredients until crumbly. Pour over top of batter in the pan.
Bake for 35-40 minutes. Let cool and drizzle with a simple glaze- 3/4 cup powdered sugar + 1 TBSP melted butter + 2 tsp milk, all whisked together.