For the topping, in a medium bowl, mix flour, sugar, and cinnamon. Add butter or margarine and mix with a fork or pastry cutter until crumbly and most of the crumbs are pea-sized. Refrigerate while preparing muffin batter.
Preheat oven to 375 degrees F. Generously spray muffin tins with nonstick spray. (Do not use paper muffin cup liners.)
In large bowl, combine flour, baking soda, baking powder, and salt. Set aside.
In another bowl, combine mashed bananas, sugar, slightly beaten egg, and melted butter or margarine. Mix well. Fold into dry ingredients just until moistened.
Fill greased muffin cups two-thirds full. Using hands, arrange coarse, pea-sized crumbs over muffin batter.
Bake at 375 degrees for 18 to 20 minutes or until muffins test done with a cake tester. Cool in pan 5-10 minutes before removing to a wire rack. Serve warm or at room temperature.
Note: If desired drizzle with a powdered sugar drizzle after muffins are cool.
Mix all ingredients together with a fork until smooth, using the minimum amount of liquid. Add the last tablespoon slowly bit by bit, stirring, until desired consistency is reached.