Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or lightly grease it.
In a large mixing bowl, combine whole wheat flour, rolled oats, vegan protein powder, ground flaxseed, coconut sugar, baking powder, baking soda, and salt. Stir well to combine.
In a separate bowl, whisk together almond milk, applesauce, melted coconut oil, vanilla extract, and mashed banana until smooth.
Pour the wet ingredients into the dry ingredients and gently fold together until just combined. Do not overmix.
Fold in the chopped walnuts evenly throughout the batter.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 22-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.