Preheat your oven to 325°F (165°C) and grease a 9x5-inch loaf pan with nonstick spray or line it with parchment paper.
In a large bowl, whisk together the mashed bananas, melted oil, honey, eggs, milk, and vanilla until smooth and well combined.
Sprinkle the whole wheat flour, baking soda, salt, and cinnamon over the wet ingredients and fold gently with a spatula until just combined (do not overmix).
If using, gently fold in the walnuts or chocolate chips until evenly distributed throughout the batter.
Pour the batter into the prepared loaf pan and smooth the top with the spatula.
Bake for 50–55 minutes, or until a toothpick inserted in the center comes out clean (cover with foil at the 30-minute mark if browning too fast).
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.