Preheat the oven to 165 degrees. If necessary, grease all 12 cups of your muffin tin with non-stick cooking spray.
In a large bowl, beat the sunflower oil, natrena and agave syrup together with a whisk. Add the eggs and beat well. Mix in the mashed bananas and milk, followed by the baking soda, vanilla extract, salt and cinnamon.
Add the flour and oats to the bowl and mix with a large spoon, just until combined. If you’d like to add any additional mix-ins**, like nuts, chocolate or dried fruit, fold them in now.
Divide the batter evenly between the muffin cups, filling each cup about two-thirds full. Add a slice of banana on top. Bake muffins for 25 to 30 minutes, or until a toothpick inserted into a muffin comes out clean.
These muffins will keep at room temperature for up to 2 days, or in the refrigerator for up to 4 days.