Position the oven rack in the lower third to avoid over-browning the bread's top and heat the oven to 350°F (177°C). Grease a 9×5-inch loaf pan with non-stick spray and set it aside.
You can mix the ingredients manually or with an electric mixer. If using a mixer, either handheld or stand, attach a paddle or whisk and blend the mashed bananas, oil, and eggs on medium-high until they are well mixed. Otherwise, just use a whisk. Include the sweetener, milk, and vanilla extract, and continue to beat or whisk until everything is well incorporated. Then set this mixture aside.
In a separate bowl, combine the whole wheat flour, almond flour, baking soda, cinnamon, and salt. Gradually add this to the wet mixture, beating or stirring by hand until just combined. If using, gently fold in any additional ingredients, like chocolate chips.
Transfer the batter to the prepared loaf pan. Bake it for 60-65 minutes. To prevent excessive browning, tent the bread with aluminum foil at the halfway point. The bread is ready when a toothpick inserted in the middle comes out mostly clean. Start checking for doneness around 55 minutes, and continue to check every 5 minutes thereafter.60–65
After baking, let the bread cool in the pan on a wire rack until it reaches room temperature. Only then should you slice it and serve it.
For storage, keep the banana bread covered at room temperature for up to 2 days, or refrigerate it for up to a week. It often tastes better on the second day as the flavors have had time to meld.