Preheat oven to 350 F.
Thoroughly spray the inside of a 12-14 cup Bundt pan with oil. Optional: after oiling, sprinkle a little sugar into the pan and add the chopped pecans to the bottom (will be the top).
In a small bowl, mix together the ground flax and water. Set aside.
In a medium mixing bowl, use a potato masher or pastry cutter to mash the bananas. They should be mostly mashed with very few large pieces. You can also use a stand mixer for this part.
Melt the butter. Add the maple syrup, oat milk, melted butter, fresh ginger, and vanilla to the mashed bananas. Mix well. Set aside.
In a large mixing bowl, whisk together the flours, baking power, salt, cinnamon, ginger powder, and ground nutmeg. Whisk for longer than you think you need to. The baking powder needs to be evenly distributed for an even rise.
Make a well in the center of the dry ingredients. Pour in the wet ingredients, not the soaked flax yet. Use a spatula to fold the dry ingredients into the wet. Stop once it is mostly mixed and only some dry is visible.
Fold in the soaked flax. If you are adding nuts, seeds, or dried fruit this is the stage to do so. No dry ingredients should be visible, but stop folding as soon as they are gone. Be careful to not overmix your batter. Overmixing creates gluten which makes your bread tough and too dense.
Spoon the batter into your prepared Bundt pan. Bake for 45-50 minutes. A cake tester or toothpick should come out clean. If you have baking thermometer, the center should be at least 195 F.
Remove from oven and let cake sit in pan for 10 minutes. Invert onto a wire rack and let cool completely. Store covered or well wrapped on the counter for up to 5 days or freeze for longer term storage. Refrigerating your breads dry them out.