Preheat the oven to 350 F, line a muffin pan with liners.
Mix flour, baking soda, baking powder and cinnamon in a bowl, set aside.
Whisk melted butter, mashed bananas, granulated sugar, and plain yogurt in a large bowl.
Add in the egg and vanilla, mix well.
Add in the flour mixture and mix. Add in the walnuts and mix.
To make the strudel, mix all the ingredients in a bowl until it forms crumbles.
Divide the batter among the muffin cups and top with strudel.
Bake in the oven for 20 minutes until the tester comes out clean or with very little crumb.
Let cool and serve.