Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan or line it with parchment paper for easy removal.

In a large mixing bowl, combine the yellow cake mix and vanilla pudding mix. Add eggs, vegetable oil, and water. Mix until smooth and lump-free, taking care not to over-mix.

Fold in the drained crushed pineapple, shredded coconut, and chopped nuts if using, ensuring they are evenly distributed.

Pour the batter into the prepared baking pan, smoothing the top. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

While the cake is still warm, poke holes all over the top with a fork and drizzle the reserved pineapple juice over the cake to add moisture and extra pineapple flavor.

Let the cake cool completely in the pan before slicing. Serve the squares as they are or garnish with additional shredded coconut or a dusting of powdered sugar.