In a high speed blender or food processor, pulse the banana, egg, cocoa powder and chopped zucchini until a very fine batter is formed. Grease a small cereal bowl or mug very well. Pour the batter in there and cook in the microwave for 60 seconds or longer, depending on desired texture. Pour batter in an oven safe dish and bake for 10-12 minutes on 180 degrees celsius for 10-12 minutes, until desired consistency.