Coat the inside of a 5- to 6-quart slow cooker with cooking spray. Add a parchment round or slow-cooker liner if desired for easier serving and cleanup.

Whisk the yellow cake mix, eggs, vegetable oil, and undrained crushed pineapple together in a large bowl just until combined. A few small lumps are fine, so avoid mixing longer than necessary.

Fold in the shredded coconut and optional chopped pecans or walnuts with a spatula. Stop folding as soon as the add-ins are evenly distributed.

Spread the batter evenly in the prepared slow cooker. Smooth the surface so the cake cooks at a consistent rate from edge to center.

Cover and cook for 2 to 3 hours on HIGH or 3 to 4 hours on LOW. Begin checking near the shorter end of the range, keeping the lid closed as much as possible.

The cake is ready when the center no longer jiggles and a toothpick inserted in the middle comes out with only a few moist crumbs. If using a thermometer, look for approximately 200 to 210°F in the center.

Turn off the slow cooker, remove the lid, and let the cake stand for 10 to 15 minutes. Slice and serve warm or at room temperature with your preferred topping.