Grease the insert of your slow cooker with butter or non-stick spray. If using, place a slow cooker liner for easy removal. Turn on the slow cooker to HIGH setting (or LOW for a longer cook).

In a large mixing bowl, thoroughly mash the ripe bananas. Add the melted butter (or coconut oil), granulated sugar, brown sugar, beaten eggs, vanilla extract, and the reserved pineapple juice. Mix until just combined. Don't overmix here, we just want to wake up those flavors.

In a separate smaller bowl, whisk together the flour, baking soda, salt, and cinnamon (or allspice). This ensures even distribution of the leavening agent.

Pour the dry mixture into the wet mixture. Gently fold until *just* combined. A few streaks of flour are acceptable; overmixing develops gluten and can lead to a tougher loaf.

Gently fold in the well-drained crushed pineapple, shredded coconut, and chopped macadamia nuts. Ensure the pineapple is well-drained to avoid excess moisture.

Pour the batter evenly into the prepared slow cooker. Cover and cook on HIGH for 3-4 hours or LOW for 6-8 hours, or until a wooden skewer inserted into the center comes out clean or with a few moist crumbs attached. Start checking at the 3-hour mark on HIGH (or 6-hour on LOW) to avoid overcooking.

Turn off the slow cooker and let the loaf cool in the insert for 15-20 minutes before carefully lifting it out onto a wire rack to cool completely. Allowing it to cool helps lock in that crucial moisture.