Prep your pan and oven: Preheat the oven to 350°F (175°C).
Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal.
Mash the bananas: In a large bowl, mash the bananas with a fork until mostly smooth with a few small lumps. You should have about 1 1/2 cups.
Mix the wet ingredients: Whisk in the melted butter, oil, granulated sugar, brown sugar, eggs, and vanilla until smooth and glossy.
Combine the dry ingredients: In a separate bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon.
Bring it together: Add the dry ingredients to the wet. Stir gently with a spatula until just combined. Do not overmix—a few streaks of flour are okay.
Fold in the nuts: Add the chopped walnuts or pecans (and any optional add-ins).
Fold just until evenly distributed.
Fill the pan: Pour the batter into the prepared loaf pan and smooth the top. For a pretty finish, sprinkle a few extra nuts on top.
Bake: Place on the center rack and bake for 55–70 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs but no wet batter. If the top browns too quickly, tent loosely with foil during the last 15 minutes.
Cool: Let the loaf cool in the pan for 10–15 minutes, then lift it out with the parchment and cool completely on a wire rack before slicing.
This helps the crumb set and stay moist.
Slice and enjoy: Use a serrated knife for clean slices. Serve warm or at room temperature, plain or with a pat of butter.