Preheat the oven to 350°F. Using the butter wrapper, grease a 9x13 baking dish. Set aside.
In a medium bowl, add the diced apples, coconut sugar, salt, and pumpkin pie spice. Stir to combine until the apples are evenly coated. Transfer to the pan and spread into an even layer.
In the same bowl you mixed the apples in, add the cake mix, melted butter, yogurt, and milk. Stir until combined. The batter will be very thick. Using a spoon, dollop the batter all over the fruit, distributing it as evenly as possible.
Transfer to the oven and bake on the middle rack for 45 to 50 minutes, until the apples are bubbly on the bottom and the “cake” is golden brown. Remove from the oven and allow to cool before cutting. Slice into 12 squares.
Serve warm with a scoop of vanilla ice cream.