Preheat the oven to 400 degrees F. Line a baking sheet with foil.
Add the butter, brown sugar, pineapple and salt and pepper to a saucepan. Simmer on medium heat, while stirring, until syrupy, about 5 minutes.
Place the squash on the prepared baking sheet cut side up and spoon the pineapple mixture into the cavity. Brush any of the exposed squash with the mixture and dust with ground cinnamon. Bake until golden brown and tender, about 1 hour.