Preheat oven to 325°F. Lightly oil 9-inch Bundt pan.
In a large bowl combine flour, sugar, baking powder, baking soda, xanthan gum and salt. Whisk thoroughly, set aside.
In another bowl mash bananas, add eggs, oil and vanilla. Mix thoroughly.
Add the wet ingredients to the dry ingredients and stir until combined.
Fold in nuts if using.
Fill Bundt pan and bake in preheated oven for 45-50 minutes until browned and starting to pull away from the sides of the pan. Cover with foil if the cake is brown on top but not quite cooked in the center. Continue cooking until done.
Cool completely on a wire rack.
Invert cake onto serving platter. Top with chocolate glaze and banana slices.