Preheat oven to 350 degrees F (176 C) and lightly butter/grease two standard 9-inch cake pans. Dust with gluten-free flour and and remove excess. Set aside.

Add chickpea brine to a large mixing bowl and beat on high for 2-3 minutes until light and airy and loose peaks form. Then add coconut sugar a little at a time and continue beating until light and fluffy and semi-firm peaks form.

Add mashed banana, maple syrup, pumpkin puree, oil, sea salt, baking soda, baking powder, cinnamon, and pumpkin pie spice and beat or whisk to combine (see photo). Add water or unsweetened almond milk and apple cider vinegar and beat/whisk again.

Add gluten-free oats, almond flour, and gluten-free flour blend and stir with a wooden spoon or whisk. The batter should be semi-thick but pourable. If too thick add more water or almond milk. If too thin, add more almond flour or gluten-free flour blend.

Divide between cake pans and bake for 45 minutes - 1 hour, or until deep golden brown and a toothpick inserted into the center comes out completely clean.

Remove from oven and let rest in pans until completely cool. Once cooled, gently loosen the sides with a butter knife and use a plate to invert and flip the cakes out of their pans. Transfer to a serving plate or cake stand and frost with desired frosting of choice.

If frosting with cream cheese frosting, store in the refrigerator up to 3 days. If frosting with buttercream, store at room temperature up to 3 days. Freeze to keep fresh for up to 1 month (though best when fresh).