Preheat the oven to 350˚ F and spray an 8x8 inch with oil.
Prepare the crumb mixture: in a food processor, add the flour, cinnamon, seeds or nuts, ground flax seed, Stevia, coconut oil, and maple syrup. Pulse process a couple times until mixed well and crumbly. Set aside.
In a medium size bowl, whisk together the flour, ground flax seed, baking powder, baking soda, and salt.
In a larger bowl, mash bananas well, then mix in the maple syrup, vanilla, oil, and lemon juice or vinegar. Once mixed well, add in the dry ingredients and mix together.
Pour a little less than half the batter into the pan and spread it out. Sprinkle this layer with 1/2 the crumb mixture. Pour the rest of the batter on top of this and carefully spread out. Top the batter with the remaining crumb mixture.
Bake in the over for 20-25 minutes or until nicely browned and toothpick inserted in the center comes out mostly clean.
Let cake cool in the pan a bit before cutting and serving warm. Enjoy!