Preheat oven to 350 degrees F (176 C) and line a standard muffin tin with paper cupcake wrappers (if subbing a different size pan, adjust cook time as needed).
To a large mixing bowl add banana, flax egg (flaxseed meal and water) and mash to combine, leaving only a few chunky pieces. You want it pretty smooth.
Add baking soda, coconut sugar, maple syrup, tahini, sea salt, vanilla, and avocado oil and whisk vigorously to combine. Then add cocoa powder and whisk again to combine.
Add gluten-free rolled oats and stir to combine. Then add almond flour a little at a time and stir to combine. You're looking for a scoopable batter that's still moist (see photo). If too dry, thin with a bit of water or dairy-free milk. If too wet, add more almond flour a little at a time. Lastly, add chocolate chips and stir to combine.
Divide batter between muffin tins, filling almost all the way to the top (as recipe is written, about 11 muffins — adjust amounts as needed if adjusting serving size). Option to sprinkle on a few more chocolate chips before baking for more chocolate flavor.
Bake on the center rack for 25-30 minutes or until risen. When cooked, a toothpick inserted into the center will come out clean.
Let rest in the pan for 5 minutes, then transfer muffins to a cooling rack to let cool completely. The wrappers come off more easily and the texture is best when completely cooled.
Store leftovers covered at room temperature for up to 4-5 days, or in the freezer for up to 1 month.
*Nutrition information is a rough estimate. *15 minutes prep includes 10 minutes for making the batter and 5-minute cooling time (although a 10- to 15-minute cooling time is ideal).