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. Put aside while preparing muffin batter.
For the muffins, in large bowl, combine dry ingredients. Set aside.
In another bowl, combine mashed bananas, sugar, slightly beaten egg and melted butter or margarine. Mix well.
Stir into dry ingredients just until moistened.
Fill greased muffin cups two-thirds full. (Do not use paper muffin cups!)
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 10 minutes before removing to a wire rack.