Preheat Oven to 425F
Grease & flour loaf pan, set aside
Make streusel topping: in a small bowl, mix together brown sugar, sinnamon & walnuts; set aside
In a large bowl, add flour, baking powder, salt and cinnamon. Mix until combined
In a medium bowl, whisk together eggs, brown sugar, and granulated sugar until combined.
Whisk in milk, oil, mashed bananas, and vanilla.
Fold wet ingredients into dry ingredients, mix just until all flour is combined; *Don't Over-mix. Batter should be thick and lumpy.
Pour batter into prepared loaf pan. Sprinkle with streusel topping.
Bake muffins at 425F for 5 minutes, reduce temperature to 375F and bake for 25 minutes