Preheat your oven to 350°F (175°C). Lightly grease a 9x5-inch loaf pan or line it with parchment paper.
In a small bowl, stir together the flaxseed and water. Set aside to thicken.
In a large mixing bowl, combine the mashed bananas, vegetable oil, granulated sugar, almond milk, and flaxseed mixture. Stir until well combined.
Gradually add the all-purpose flour, baking soda, salt, and cinnamon to the wet ingredients, stirring until just combined. Be careful not to overmix; a few lumps are okay.
Fold in the chopped walnuts.Pour the batter into the prepared loaf pan, spreading it out evenly.
Bake in the preheated oven for 60-75 minutes, or until a toothpick inserted into the center comes out clean. If the top starts to brown too quickly, you can cover it loosely with aluminum foil for the last 10-15 minutes of baking.Allow the banana walnut bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.