Pre-heat the oven to 375 degrees and grease 10 muffin cups (or line with muffin papers). In a large bowl mix 1 ½ cups flour, baking powder, baking soda, and salt.
In a separate bowl beat together bananas, sugar, egg, and melted butter. Stir banana mixture into the flour mixture just until moist and combined. Spoon batter into prepared muffins cups.
To make streusel- in a small bowl mix brown sugar, 2 tablespoons flour, and ground cinnamon. Cut in 1 tablespoon of butter until mixture is crumbly. Sprinkle streusel over the top of the muffins.
Place into the oven and bake for 18 to 20 minutes or until a toothpick inserted comes out clean.