Preheat oven to 175*C
In a small bowl, mash over-ripe plantain with a fork until all large lumps are gone (some small are ok).
Add egg, coconut oil, and vanilla and mix by hand.
In a medium bowl, mix the oat flour, coconut flour, psyllium husk powder, baking soda, baking powder, and salt.
Pour wet ingredients into dry and stir will until everything is combined.
If using nuts and/or berries, add them in and stir just until mixed.
Pour batter equally into greased muffin cups (I use coconut oil).
Bake for 20 minutes, or until toothpick come out clean with test.
Serve immediately or keep in refrigerator for up to 5 days, or freeze unused portion to use later.