Preheat the oven to 350 degrees.
Prepare a muffin pan with cupcake papers.
Prepare the streusel mixture by combining the ingredients together with a fork.
In the bowl of an electric mixer, add the bananas and mix until well mashed.
Add the remaining ingredients and mix until combined.
Place mixture into muffins cups, distributing evenly and taking care not to overfill.
Top with the streusel mixture.
Bake for 8-12 minutes or until a toothpick inserted comes clean. As all ovens vary greatly, you may need more or less baking time. Keep an eye on them.