**Preheat the Oven:** Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish or line it with parchment paper.
**Mix the Batter:** In a large mixing bowl, combine the yellow cake mix and the entire can of crushed pineapple (including juice). Stir until just combined.
**Pour and Bake:** Pour the batter into the prepared baking dish, spreading it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
**Cool:** Let the cake cool completely in the pan on a wire rack.
**Garnish and Serve:** Sprinkle shredded coconut on top (if using) or spread whipped topping over the cake. Serve and enjoy!