Whisk the milk, cocoa powder, turbinado sugar, and almond extract together in a saucepan over medium-low heat until the sugar has dissolved; bring the mixture to a simmer.
Stir the mashed banana and oatmeal into the milk mixture; cook at a simmer until the oatmeal is thickened and the banana has broken up slightly, about 5 minutes. Fold the slivered almonds into the oatmeal to serve.
