In a medium-sized bowl combine butter, brown sugar, and cinnamon. Add the flour and mix until fully incorporated. Mixture will be mushy and this is normal! The next step will fix that.
Using a fork, continually mix until mixture is crumbly, breaking apart any overly large clumps as necessary (this will take a minute or two). Set aside.
In a large bowl combine bananas, sugar, cinnamon and salt. Beat in the oil, eggs, and vanilla extract.
Add the flour and baking soda and gently mix until combined. Do not overmix!
Scoop the batter into the muffin pan filling the cups two-thirds of the way full.
Top each muffin with just enough crumb topping to fully cover the tops, gently pressing it into the batter as you go.
Bake for 16 – 18 minutes until the centers are fully baked and a toothpick inserted comes out clean.
Cool in pan 5 minutes then transfer to a wire rack to cool completely.
In a small bowl mix together the powdered sugar, cream/milk, and vanilla extract (if glaze is too thick add a splash more cream/milk).
Drizzle over the fully cooled muffins then serve.