Rinse, then cut pineapple into 2-inch pieces. Place pineapple in a food processor; process until smooth. Add water if necessary. If you are using canned pineapple, add some of the juice until the pineapple becomes smooth.
Pour mixture into a freezer safe bowl or dish. Cover and freeze 1 hour or until firm.
Serve on top of graham cracker and garnish with mint sprigs, if desired.