Set aside a few cornflakes for the garnish. Roast the oatmeal in a dry pan for about 3 minutes. Peel the banana and chop it roughly.
Puree everything together, including the cooled oat flakes, in a tall vessel with a magic wand to make a milkshake. Pour the shake into 1 large, pretty glass and sprinkle with the cornflakes and cinnamon.