Preheat oven to 450°F.
For the streusel topping, in a medium-sized bowl, combine butter, sugar, and cinnamon. Add the flour. Using a fork, mix until the mixture is crumbly. Set aside.
In a large bowl, mash the bananas. Add sugar. Beat in the oil, eggs, and vanilla extract.
Add the flour, baking powder, cinnamon, and salt. Mix until just combined.
Scoop the batter into the muffin tin. Each one will be full, and that’s okay - it makes for tall muffins.
Top each muffin with just enough streusel topping to fully cover the tops, gently pressing it into the batter as you go.
Bake at 450°F for 8 minutes and then reduce the temperature to 350°F for the remaining 20-22 minutes.
Cool in pan for 5 minutes, then transfer to a wire rack to cool completely.
For the glaze, whisk the ingredients together until smooth. The icing should not be too runny. Drizzle over the cooled muffins. Enjoy!