Preheat the oven to 350°F and line a 12-cup muffin tin with liners. Set aside.
In a large bowl, mash the bananas with a fork. Add the sugar and softened butter, then mix with an electric hand mixer until well combined. Beat in the eggs and vanilla until smooth.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually incorporate the dry ingredients into the banana mixture, stirring until fully combined. Use an ice cream scoop to evenly distribute the batter into the muffin cups.
In another bowl, mix the streusel topping ingredients, then sprinkle over each muffin.
Bake for 20 minutes. Remove from the oven and let cool for at least 10 minutes before taking the muffins out of the pan. Serve and enjoy!