Preheat the oven to 350. Grease the loaf pan and place a sling of parchment paper in the middle for easy removal.
In a large bowl make flax eggs. Whisk and set aside for 10 minutes to gel. If you are using eggs, add them to a bowl and whisk. Add bananas and mash well until no lumps remain. Whisk in squash purée, olive oil and vanilla. Add sugar, baking powder, xanthan gum, salt, cinnamon and pumpkin pie spice and whisk to combine.
Finally, fold in flour and mix until no dry ingredients remains. Add in chocolate chips and walnuts. Transfer batter in loaf pan and smooth top with spatula. Sprinkle more walnuts and chocolate chips evenly over the top. Slice your 4th banana in half and press into batter (optional).
Place in a preheated oven and bake for 45-50 minutes until a toothpick comes out clean. Sprinkle with Maldon sea salt (optional) to finish. Transfer to a wire rack and allow it to cool in the pan for 10 minutes. Remove it from the pan using the parchment paper sling. Wait for it to cool completely before slicing.
*Macros are provided as an estimate for convenience. Your final numbers will vary depending on ingredient brands, substitutions, and how you portion the recipe.