Prep your pan and oven. Heat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal.

Toast the walnuts. Spread the chopped walnuts on a baking sheet and toast in the preheating oven for 5–7 minutes until fragrant. Let cool. This step boosts flavor and crunch.

Mash the bananas. In a large bowl, mash the bananas with a fork until mostly smooth with a few small lumps. Measure to ensure you have about 1 1/3 cups.

Whisk the wet ingredients. Add eggs, oil, granulated sugar, brown sugar, and vanilla to the bananas. Whisk until the mixture is well combined and glossy.

Combine dry ingredients. In a separate bowl, whisk flour, baking soda, baking powder, salt, and cinnamon. Mixing them first helps distribute the leavening evenly.

Bring it together. Add the dry mixture to the wet mixture. Stir gently with a spatula until just combined. A few small streaks of flour are fine.

Fold in the walnuts. Add the toasted walnuts (and any optional add-ins). Fold gently. Do not overmix or the bread can turn tough.

Fill the pan. Pour the batter into the prepared loaf pan and smooth the top. For a pretty finish, sprinkle a few extra walnuts on top.

Bake. Bake for 55–70 minutes, depending on your oven. Start checking at 55 minutes. A toothpick inserted in the center should come out mostly clean with a few moist crumbs, not wet batter.

Cool properly. Let the loaf cool in the pan for 10–15 minutes, then lift it out and cool completely on a wire rack before slicing. This keeps the crumb from tearing.