Preheat oven to 350°F/175°C. Spray a large loaf pan** with vegetable spray.
In a food processor, add the bananas, vegan butter, sugar, vanilla, milk, flax, and cornstarch. Pulse in short bursts until combined, leaving some banana chunks. Set aside.
In a large bowl add the flour, baking soda, baking powder, and salt. Stir to combine.
Fold the chopped toasted nuts into the flour mixture. Stir until the nuts are coated. Add the wet ingredients. Stir until just combined.
Pour the batter into your prepared pan and bake for 50 to 60 minutes, until the crust is golden brown and a toothpick inserted in the center comes out clean.
When done, remove the pan from the oven and cool for 10 minutes. Then invert on a wire rack to cool completely.
To store, let the loaf cool completely and wrap in plastic wrap or in an airtight container. It will keep at room temperature for up to 4 days, refrigerated for up to 7 days, or frozen up to 2 months. To thaw, leave the loaf at room temperature. Then heat up individual slices in a toaster oven or microwave.