Preheat the oven to 200C/390F (or 180C fan forced) and prepare the muffin tray or quarter baking sheet by lining with muffin wrappers/baking paper.
Add the eggs and coconut oil to the blender or food processor. Then add in the bananas, broken in to pieces. If using a blender: blend these ingredients first, followed by all remaining ingredients except the mix-ins/toppings. If using a food processor: all of the ingredients except the mix-ins/toppings can be added in one step and blended thoroughly. If there are some lumps in the batter, use a tamper with the blender running or run the food processor again. Add most of the mix-ins to the batter and stir with a spatula - this can be done in the blender or food processor after removing the blade. If using frozen blueberries they can stain the batter if you mix them in, I recommend to just place them manually with your fingers in the next step after pouring the batter.
Pour/scoop the batter in to the prepared muffin tin/s. Garnish with remianing mix-ins. Spray the top of the muffins with coconut oil to prevent burning.
Bake on the middle rack for 15 minutes, reduce the oven temperature to 180C/350F (160C fan forced), loosely tent with foil and turn the tray/s around.
Bake for a final 15 minutes or until a skewer comes out clean. If using a baking sheet instead of a muffin tray, bake for a ttoal of 40 mins (turning halfway) Ovens can vary quite a lot in temperature, so start with the recommended duration and check on them to ensure they aren't burning. They are done when a skewer comes out clean.
Immediately remove muffins from the tray and cool on a rack.
Can be stored in the refrigerator for up to 5 days. These also freeze well for up to 3 months.