Preheat the oven to 400 degrees F. Use non-stick cooking spray to coat 12 muffin cups. In a medium bowl, whisk eggs and brown sugar until smooth. Add bananas, wheat bran, bananas, vanila and oil and whisk. In a separate large bowl, whisk together the whole wheat flour, all purpose flour, baking powder and baking soda, cinnamon, and salt. Create a well in the flour mixture and add the wet ingredients and stir. Do not overmix. Add chocolate chips if desired. Place batter by spoonfuls into the muffin cups until full, and sprinkle with walnuts if desired. Bake until golden brown and a toothpick comes out clean. Let cool for 5 minutes before serving.