Preheat oven to 200 deg c (180deg if fan forced), and grease a muffin tray with some coconut oil.
Wash feijoas, then remove the tops, and chop up (leave the skin on). Add to a bowl and mix in the brown sugar, egg, melted coconut oil, and milk.
Sift in flour, baking powder, and cinnamon, and gently combine. Don’t over mix, as they will get a bit tough.
Spoon mixture evenly into muffin tray.
Cook for 18-20 minutes, or until cooked through.