In a large bowl, mix the flour, baking soda, baking powder, and salt. In another bowl, beat together the bananas, sugar, egg, and melted butter. Stir the flour mixture into the banana mixture just until moistened. Spoon the batter into the prepared cups, filling evenly.
To make the crumb topping: In a small bowl, mix together the brown sugar, flour and cinnamon. Cut in the butter with with a fork or pastry cutter until the mixture resembles coarse crumbs. Sprinkle over the muffins.
Bake in the preheated oven for 18-20 minutes for jumbo muffins or 13-15 minutes for regular muffins, or until the top is golden brown and a toothpick inserted in a muffin comes out clean.
Let the muffins cool for 5 minutes before removing from the tin.
Notes
Nutrition information provided as an estimate only. Various brands and products can change the counts. Any nutritional information should be used as a general guide.