Preheat oven to 375 degrees. Line a muffin pan with 10 liners or with non-stick spray.
Start with a large bowl and whisk together the batter flour, baking soda, baking powder and salt. Set aside.
In another bowl, mash the bananas and mix in the sugar, egg and melted butter.
Add the banana mixture into the flour mixture; mix everything together until just combined. Scoop the batter and fill each liner about ¾ of the way full. Set aside.
In a small bowl, mix together the crumb topping brown sugar, flour and cinnamon. Cut in the butter and mix until the mixture is course and crumbly. Spread the mixture over all of your muffins.
Bake for 15-20 minutes. You can test with a toothpick for doneness.