Preheat oven to 350 degrees F (175 degrees C). Line a muffin tin with paper liners.
Whisk rice flour, coconut flour, cornmeal, xanthan gum, baking powder, baking soda, and salt together in a large bowl.
Whisk water and egg replacer together in a glass measuring cup. Add enough applesauce to make 1/4 cup. Transfer mixture to a blender; add oat milk, maple syrup, baby spinach, oil, and vanilla extract. Blend until smooth.
Pour spinach mixture over the flour mixture; mix until just combined. Fold mashed bananas and chocolate chips into the batter.
Scoop batter into the prepared tin, filling each cup 3/4 full.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 25 minutes. Transfer to a wire rack to cool completely.
