In a mixing bowl, combine cooked oatmeal, 3/4 cup milk, chocolate syrup and sugar; mix well.

Pour into an ice cube tray; freeze. Remove frozen cubes from ice cube try and store in plastic bag in freezer until needed.

When ready to make the shake, combine banana and remaining 1/4 cup milk in container of electric blender. Blend until smooth.

Remove frozen oatmeal cubes from freezer. Turn blender on medium-high speed; add frozen cubes to mixture in blender, one at a time, until all cubes are used and mixture is well blended.

(Add a little more milk, if necessary for easier blending.) Add peanut butter; blend until well mixed.