Preheat the oven to 180°C. Line a standard loaf tin with baking paper.
Mash the bananas in a large bowl. Add the egg, vanilla extract and oil and mix well.
Stir in the cocoa powder until evenly combined.
Add the oats, self-raising flour and baking powder and gently mix until just combined.
Fold in the strawberries and goji berries, reserving a few pieces of strawberry for the top if desired.
Pour the mixture into the prepared loaf tin and smooth the surface.
Bake for 40–50 minutes, or until a skewer inserted into the centre comes out clean.
Leave to cool in the tin for about 10 minutes, then transfer to a wire rack to cool completely before slicing.