In a large bowl, mix together 1 1/2 cups flour, baking soda, baking powder and salt. In another bowl, beat together bananas, sugar, egg and melted butter. Stir the banana mixture into the flour mixture just until moistened. Spoon batter into prepared muffin cups.
In a small bowl, mix together brown sugar, 2 tablespoons flour and cinnamon. Cut in 1 tablespoon butter until mixture resembles coarse cornmeal. Sprinkle topping over muffins.
Bake in preheated oven for 18 to 20 minutes, until a toothpick inserted into center of a muffin comes out clean.
When spooning batter into prepared muffin cups, filling them about 2/3 the way full. If you are just making 12 muffins, fill them a little fuller, but not too much to avoid overflowing when they bake up.