Step 1: Preheat your oven to 350°F (175°C).
Step 2: Thoroughly grease a 9x13-inch baking dish.
Step 3: In a large mixing bowl, combine the yellow cake mix, the first can (20 oz) of crushed pineapple in juice (undrained), 3 large eggs, and 1/2 cup vegetable oil.
Step 4: Beat the mixture with an electric mixer on medium speed for 2-3 minutes, until it's fully blended and smooth.
Step 5: Pour the batter evenly into your prepared baking pan.
Step 6: Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Step 7: Remove the cake from the oven and let it cool completely in the pan on a wire rack. This is crucial before adding the topping.
Step 8: In a medium bowl, combine the thawed whipped topping, instant vanilla pudding mix, and the second can (20 oz) of crushed pineapple in juice (undrained).
Step 9: Gently fold and mix until all ingredients are smooth and well combined.
Step 10: Once the cake is completely cool, spread the pineapple-pudding topping evenly over the entire surface.
Step 11: Refrigerate the cake for at least 1 hour before serving to allow the topping to set and the flavors to meld. For best results, chill for 2-3 hours.