Make the crumb topping by mixing together chocolate chips, brown sugar, flour and cinnamon in a medium bowl. Cut in the butter until it resembles coarse crumbs and set aside.
Step 2
Whisk flour, baking powder, baking soda and salt in another bowl to remove any lumps then set aside.
Step 3
Cream butter, brown sugar and vanilla in a bowl until light and fluffy. Add the egg and then the mashed banana.
Step 4
Add flour mix into the wet ingredients alternately with Greek yogurt, starting and ending with sifted ingredients then beat until smooth. Don't over mix.
Step 5
Pour into the cake pan, sprinkle with the reserved streusel crumb topping.