Preheat the oven to 180 degrees C/350 F and line a muffin tray with muffin cases. Alternatively, you can grease it lightly with vegan butter.
Prepare flax eggs by stirring together ground flaxseed with the water, and setting aside for 5-10 minutes.
In a large mixing bowl, stir together the rice flour, chickpea flour, baking powder, baking soda and xanthan gum.
In a separate mixing bowl, mix together the olive oil, mashed banana, apple cider vinegar, maple syrup, and the flax eggs.
Add the wet ingredients to the dry, and mix together until evenly combined. Add the chocolate chips and mix once more.
Distribute the batter evenly between the muffin cases, filling them about ¾ of the way. Bake in the preheated oven for 25-30 minutes, until a toothpick comes out clean from the centre.
These muffins can be kept on the counter, covered, for up to 2 days. Alternatively, you can store them in the fridge in an airtight container for up to 5 days. Reheat in the microwave, or by placing in a preheated oven for 5-10 minutes.
Freeze these muffins for up to 2 months in a freezer-friendly bag or container. Leave to thaw fully in the fridge overnight before reheating in the microwave or in a preheated oven.