Preheat your oven to 350 degrees F.In a large bowl or stand mixer with paddle attachment, add all the wet ingredients (banana, milk, vanilla, oil). Stir until combined.To the same bowl, add in all the dry ingredients (flax, oat flour, stevia, salt, nutmeg, cocoa, baking soda/powder)Stir together until mixed and place batter in greased muffin tins or with silicone muffin liners.Bake for 20 - 23 minutes until muffins are set on top and a toothpick comes clean.Allow to cool and store in an airtight container. Will last about a week in the fridge, or a few months in the freezer.