Puree the bananas. Mix all other ingredients with the mashed bananas. Spread the muesli mixture loosely on a baking sheet and slide it into the oven on the middle rack. Bake the muesli for 40 minutes. Turn the muesli every 10 minutes and chop briefly with a spatula. This creates smaller and larger pieces of cereal. The muesli browns a little. After 40 minutes, take the muesli mixture out of the oven and let it cool on the tray.