Lightly coat 5 half-pint canning jars with nonstick cooking spray. In a large bowl combine the first 11 ingredients (through nutmeg). Stir in oats, banana, walnuts, and raisins. Spoon into prepared jars; cover each with foil.
Add 1 cup water to a 6-qt Instant Pot; insert wire rack. Carefully place each jar on the rack. Lock lid in place. Set Instant Pot on High Pressureto cook 8 Minutes. Turn off Instant Pot; let stand 10 Minutes to release pressure naturally. Release any remaining pressure. Open lid carefully. Use hot pads to carefully remove jars to a wire rack; uncover and cool 10 Minutes. If you like, top with additional banana slices and walnuts.