Preheat oven to 375°F. In a large bowl whisk together cassava flour, brown rice flour, oats, baking powder, cinnamon, salt, and baking soda. Set aside.
In another large bowl whisk eggs until lightly beaten. Whisk in oil, coconut milk and syrup. Add egg mixture all at once to flour mixture. Add mashed bananas. Whisk until well combined (don’t worry about overmixing).
Lightly brush bottoms and sides of 20 to 22 standard size (2 ½-inch diameter) muffin cups with olive oil (if using nonstick pans this isn’t necessary) or line muffin cups with paper liners.
Spoon batter evenly into prepared muffin cups (cups will be almost full).
Bake for 14 to 17 minutes or until a toothpick inserted into center of muffins comes out clean (it’s okay if a few crumbs come up with the toothpick as long as it doesn’t look like batter on the toothpick).
Allow muffins to cool in the pans for 5 minutes. Remove muffins from pans (if not using paper liners, you may need to run a thin dull knife around the edge of the muffins to loosen them from the sides). Cool on a wire rack.
Store completely cooled muffins in an airtight container at room temperature up to 3 days or freeze up to 3 months.