Preheat the oven to 350 degrees. Line a loaf pan with parchment paper. In a small bowl, whisk together flax seed meal and water. Set aside for 5 minutes.

In a large mixing bowl, mash banana with flax egg until smooth (some clumps remain, but mostly smooth). Whisk in maple syrup, vanilla, and apple cider vinegar. Add flours, baking powder and soda. Using a spatula or wooden spoon, stir to combine until a smooth batter forms. Divide batter amongst two mixing bowls. Add cocoa powder and chocolate chunks to one to make the chocolate banana bread batter.

Alternating between batters, pour into the prepared loaf pan. Spread to evenly distribute. Take a knife and swirl around surface of the batter. (Optional): Top with a couple tablespoons of chocolate chunks and half a banana cut lengthwise.

Bake for 38-40 min. until a toothpick inserted comes out clean. Let cool for 10 minutes before transferring to a wire cooling rack. Best sliced when it has completely cooled.