As preparation, drain the pineapple tidbits and the whole pitted cherries. Spray your slow cooker.
Spread the pie filling, cherries, and half of the pineapple pieces in the bottom of a 7—or 8-qt slow cooker. Sprinkle on some cinnamon.
Next, evenly spread out the dry cake mix. Scatter the remaining pineapple pieces on top and add another dash of cinnamon. Melt the butter substitute and drizzle it over top, too.
Cover and bake the dump cake on HIGH for 1 hour. At this point, I like to flip the insert to promote more even baking, and this is optional, but I carefully fluff the top of the cake mix with a fork (don’t mix it into the fruit too much, though; it will get soggy). If you think that the cake mix is too dry, you can add a bit more of the melted butter substitute to hydrate it; just be careful not to overdo it.
Cover the pot again; place a paper towel shield with the lid on top of the towels to hold them in place. This prevents condensation from dripping onto the dessert.
Cook the dump cake for 1.5 – 2 hours longer or until ready. It is ready when the fruit is bubbly on the sides, and the topping is no longer wet but like a streusel or crumble. Remember that the cake doesn’t brown as much in the slow cooker as in the oven. It will be light and fluffy without much crispiness.
Take the lid off the dump cake and allow it to rest for a bit before serving so it has time to firm up.