Preheat the oven to 350°F. Grease a 9x5-inch loaf pan generously with nonstick cooking spray and line it with parchment paper for easy removal. Set the prepared pan aside.
In a large bowl, whisk together the 1 cup mayonnaise, 1/2 cup granulated sugar, 1/2 cup packed brown sugar, and 2 teaspoons vanilla extract until smooth. Stir in the 1 1/2 cups mashed very ripe bananas until the banana-mayonnaise mixture is evenly combined.
In a separate medium bowl, whisk together the 2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, and 1/2 teaspoon salt until evenly combined.
Add the dry ingredients to the wet ingredients and stir gently with a spatula until just a few streaks of flour remain. Fold in the 1 cup chocolate chips or 1 cup chopped walnuts, if using (or 1/2 cup of each). Don’t overmix, or the loaf can turn dense instead of tender.
Pour the batter into the prepared loaf pan and use a spatula to smooth the top. Bake for 55 to 65 minutes, or until a toothpick inserted into the center of the loaf comes out clean or with just a few moist crumbs.
Let the banana bread cool in the pan for 10 minutes. Run a knife around the edges, then turn the loaf out onto a wire rack and let it cool completely before slicing.