Grease the muffin tins or line it them with paper liners.
In a large bowl, mash the bananas until smooth.
Add the egg. Mix until well combined.
Add the coconut oil, mixing well
Stir in the flour and baking powder until the mixture is just combined.
If using, fold in the optional add-ins like grated carrots, sweet potatoes, blueberries or any other ingredients.
Spoon the batter into the prepared muffin tin, filling each cup about 3/4 full.
Bake for 15-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool completely before serving them to your dog.
Notes
Storage
Muffins can be stored in an airtight container at room temperature in for up to 5 days, or in an air-tight container in the freezer for up to 3 months.