Begin by preheating your oven to 350°F and preparing a 9x5-inch loaf pan by spraying it with cooking spray.
In a medium-sized mixing bowl, sift together the almond flour, gluten-free flour, baking powder, baking soda, and salt. Set this dry mixture aside.
In a stand mixer or with a hand mixer, cream together the shortening and sugar on medium speed for 2-3 minutes, until the mixture becomes light and airy.
Next, incorporate the eggs, vanilla extract, and milk into the mixture. Beat for 1-2 minutes, pausing halfway to scrape down the sides of the bowl to ensure everything is fully combined.
Gradually add half of the dry ingredients to the wet mixture and blend until incorporated. Then, mix in half of the mashed bananas. Repeat this process with the remaining dry ingredients and bananas, ensuring the batter is smooth and well-hydrated by alternating additions. Continue mixing for an additional 15-20 seconds until the batter is silky and consistent.
If using, gently fold in the chopped nuts or chocolate chips using a rubber spatula.
Pour the batter evenly into the prepared loaf pan. Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 5 minutes before transferring it to a wire rack to cool completely.