1. Coat a 3-quart electric slow cooker with cooking spray. Combine brown sugar and next 3 ingredients (through rum) in slow cooker. Cover and cook on LOW for 1 hour. Stir with a whisk until smooth.
2. Add pineapple, cinnamon, and banana to sauce, stirring to coat. Cover and cook on LOW for 15 minutes. Serve immediately over ice cream.
Quick tip: Fresh pineapple is a treat, but sometimes for the sake of convenience, the precut variety is worth reaching for. Either way, you can't go wrong.