In a medium bowl, combine melted coconut oil and maple syrup. Whisk until well combined. Add eggs and mix well. Add banana, vanilla and coconut milk. Mix until all ingredients are incorporated.
In a separate bowl, combine GF flour, oats, baking soda, salt and cinnamon. Mix well with a fork. Pour wet mixture into dry. Mix until just combined - do not overmix. Add fruit or nuts, mix gently. Let batter rest while you prepare your pan.
Line or grease a 12 serving regular size muffin pan. Divide batter evenly into 12 muffins, making each portion about ¾ full.
Combine sugar and cinnamon and sprinkle over muffins. Then sprinkle each muffin with oats.
Bake for about 25 minutes until tops spring back when touched. Remove to cool and serve immediately. These will store well for a few days in an airtight container in the refrigerator.