Preheat oven to 350 degrees and grease a 9x13 baking dish. In a large bowl, mix together the cake mix, pudding mix, oil, eggs, and pineapple with juices. Beat until well combined.
Transfer batter to the prepared baking dish and bake for 30-35 minutes or until an inserted tooth pick comes out clean. Allow cake to cool.
In a medium bowl, whisk together the pistachio pudding mix and cold milk until thickened (about 2 minutes). Gently fold in the whipped topping until smooth and fluffy.
Once the cake is completely cooled, spread the pistachio frosting evenly over the cake.
Sprinkle with chopped pistachios or pecans, and add maraschino cherries for a festive touch. Cover and refrigerate for at least 2 hours to let the flavors meld.
Slice, serve, and enjoy this light, fluffy, and tropical Pistachio Pineapple Paradise Cake!