Preheat your oven to 350°F (175°C) and prepare a 12-cup muffin pan.

Mash the ripe bananas in a medium-sized bowl until mostly smooth.

Grate the zucchini finely and squeeze out excess moisture with a kitchen towel.

In a large bowl, whisk together the all-purpose flour, baking soda, baking powder, fine sea salt, ground cinnamon, and optional nutmeg.

Add the neutral oil, brown sugar, eggs, and vanilla extract to the banana mixture and whisk until smooth.

Fold the grated zucchini into the wet mixture evenly.

Carefully fold the wet mixture into the dry ingredients until no dry flour remains.

Fold in any desired mix-ins like chocolate chips or nuts.

Divide the batter evenly among the prepared muffin cups, filling each about ¾ full.

Bake in the preheated oven for 16-20 minutes or until a toothpick comes out with moist crumbs.

Cool in the pan for about 5 minutes, then transfer to a wire rack to cool completely.