Preheat your oven to 350°F (175°C). Generously spray your 9x5-inch loaf pan with gluten-free baking spray, making sure to coat all the corners to prevent sticking.
In a large mixing bowl, mash the seven ripe medium bananas with a fork or potato masher until mostly smooth but still slightly chunky. This texture adds character to the bread.
Add the 1/2 cup unsweetened applesauce, softened butter, light brown sugar, egg whites, and vanilla extract to the mashed bananas. Use a hand mixer or stand mixer on medium speed to blend until smooth and creamy.
In a separate bowl, whisk together the 2 1/2 cups gluten-free flour, 1 1/2 teaspoons baking soda, and 1/2 teaspoon salt. This ensures even distribution of the leavening agent and salt.
Gradually add the dry ingredients into the wet banana mixture, mixing on low speed until just combined. Avoid overmixing to keep the bread tender.
Using a spatula, gently fold in the 3/4 cup chopped walnuts. This keeps the nuts evenly distributed without breaking them down too much.
Pour the batter into the prepared loaf pan, smoothing the top with your spatula. Bake for 60 to 70 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs attached.
Let the bread cool in the pan for 15 minutes, then transfer it to a wire rack to cool completely. Slice and serve warm or at room temperature.