Pre-heat your oven to 160 C / 320 F. Line a loaf tin with baking paper - use enough paper to go up the sides so you can easily lift out the loaf once baked.
Add the bananas and vanilla extract to the Thermomix bowl. Mix for 5 seconds / speed 5. Set aside.
Add the butter and sugar to the bowl and cream together for 30 seconds / speed 5.
Add the banana mixture and eggs to the bowl and mix for 10 seconds / speed 4.
Add the flour, cocoa powder, baking powder and bicarbonate of soda to the bowl. Mix for 20 seconds / speed 5.
Measure in 130g chocolate chips to the bowl. Use a spatula to mix them into the mixture.
Smooth the batter into your prepared loaf tin and sprinkle over the remaining 40g chocolate chips.
Bake in the oven for around 50-55 minutes, or until a skewer inserted in the middle comes away clean. (Remember that there will be melted chocolate chips in the loaf though, so don't be fooled by them!)
Use the overhanging baking paper to lift the loaf out of the tin and place on a cooling rack to cool until ready to slice and serve.