Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish or line it with parchment paper.
In a large mixing bowl, combine the yellow cake mix, pistachio pudding mix, eggs, oil, and crushed pineapple (with juice). Stir until fully combined and smooth. The batter will be slightly thick and green from the pudding mix.
Pour the batter into the prepared pan and spread it evenly. Bake for 28–32 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.
In another bowl, mix the second box of pistachio pudding with the whipped topping and remaining can of crushed pineapple (with juice). Stir until smooth and well blended. Let it chill in the fridge for 10–15 minutes to firm up slightly.
Once the cake is fully cooled, spread the chilled frosting evenly over the top.
Sprinkle with chopped pistachios and top with maraschino cherries if desired. Chill for at least 1 hour before serving for best flavor and texture.