Preheat the oven to 350°F.
Grease a 9x13-inch baking dish with nonstick cooking spray or a suitable baking grease.
In a large mixing bowl, combine the angel food cake mix, 1 box of instant pistachio pudding mix, vegetable oil, eggs, and the full can of crushed pineapple with juices.
Beat the mixture until the batter is fully combined and no dry pockets of cake mix remain.
Transfer the batter to the prepared baking dish.
Spread the batter evenly in the dish using a spatula.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Remove the cake from the oven.
Allow the cake to cool completely in the baking dish before frosting.
To prepare the frosting, add the second box of instant pistachio pudding mix and the whole milk to a medium mixing bowl.
Whisk until the pudding mixture thickens.
Gently fold in the thawed Cool Whip until the frosting is smooth and fully combined.
Spread the pistachio frosting evenly over the cooled cake.
Sprinkle chopped pistachios over the top, if desired.
Refrigerate the frosted cake for at least 2 hours before serving.
Slice into 12 servings and serve chilled.
Store any leftovers covered in the refrigerator.