Melt the chocolate chips in a microwave 20 seconds at a time until you can stir with a spoon and it is melted.
Add the bananas to a Thermomix® mixing bowl (or food processor/blender) and turn on speed 8 for 10 seconds.
Scrape down with a spatula, then turn on speed 4 for 1 minute. At about 30 seconds, begin drizzling the melted chocolate into the mixing bowl while it is mixing.