Preheat your oven to 350°F (175°C) to ensure even baking.
Lightly coat your loaf pan with gluten-free baking spray to prevent sticking.
In a large mixing bowl, mash the 7 ripe bananas until smooth, leaving some small chunks if desired for texture.
Add the unsweetened apple sauce, softened butter, light brown sugar, egg whites, and vanilla extract to the mashed bananas. Mix until well combined.
In another bowl, whisk together the gluten-free flour, baking soda, and salt to evenly distribute the leavening agents.
Gradually add the dry mixture to the wet mixture, stirring gently until just combined. Avoid overmixing; a few lumps are fine.
Gently fold in the chopped walnuts, distributing them evenly throughout the batter.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Remove from oven and let the bread cool in the pan for about 10 minutes. Transfer to a wire rack to cool completely before slicing.