Pour the Jello over the pineapple while it's in the can (there will be lots of Jello leftover so just put that in a bowl in the fridge for an afternoon snack!). Put the can in the fridge until set up. Slide a knife around to loosen it and invert it onto a plate.
Then slice each pineapple slice and eat. It's disgusting. Disgustingly good! The kids loved it and I even enjoyed it. A simple, different dessert.