Preheat oven to 190C - or 170C if using fan-forced.
Line a 12-hole muffin pan with paper cases.
Combine the self-raising flour, cinnamon and sugar in a large bowl.
Make a well.
Add mashed banana, vanilla extract, egg, yoghurt, chocolate chips and oil.
Stir until just combined.
Very gently fold through the frozen berries.
Spoon into paper cases.
Top with a couple of extra chocolate chips.
Bake for 20 to 25 minutes.
Stand in pans for 2 minutes.
Transfer to a wire rack to cool.
A toothpick inserted in the center should come out clean.
Allow the muffins to cool completely.... or just eat one while they are still warm! Why not!