Preheat oven to 350 degrees F.  Oil a 9 by 13 inch pan.

Make the streusel.  In a medium bowl, stir together the chips, coconut sugar, walnuts, and cinnamon.  Set aside.

Make the cake.  In a large bowl, stir together flour, baking soda, baking powder, salt, sugar, oil, eggs, and mashed bananas until a batter forms.

Spread half the batter in the prepared pan.  Sprinkle with 2/3 of the streusel mixture.  Top with the remainder of the batter, then the remainder of the streusel.  Press the streusel gently into the batter.  Bake 45-60 minutes until golden brown and a toothpick inserted in the center comes out clean or with a few moist crumbs.  Serve warm or cool completely in the pan.

Cake may be stored in an airtight container at room temperature for up to 4 days or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months.  Thaw at room temperature about an hour or in the microwave about 1 minute.