Pre-heat oven to 350*F.
In a large bowl, whisk together your dry ingredients, including the sweetener. Set aside.
In another bowl, whisk together the melted butter, room temperature eggs and vanilla extract.
Pour the butter mixture into the dry ingredients along with your mashed banana and sour cream.
Stir well until a thick batter forms.
Grease a 9 x 12 inch pan with oil or butter then spread half of the batter as evenly as you can over the bottom of the pan. (You can also try using a 9 x 13 inch pan for this)
Mix together your brown sugar sweetener and cinnamon for the topping then sprinkle half of it over this layer of batter. Top with half the chocolate-chips as well.
Spread the rest of your batter over the first layer as best as you can (I use my fingers to help a bit with this) then repeat the sprinkling of the brown sugar/cinnamon mixture and adding of the chocolate chips.
Bake the cake for ~40min. Cool the cake fully it it's pan on a wire rack before slicing and serving. Enjoy!