Prep the slow cooker: Lightly coat the crock with nonstick spray or use a liner.
This helps prevent sticking and makes cleanup easy.
Add the fruit base: Pour the pie filling into the bottom of the crock. Stir in the vanilla, cinnamon (if using), and a pinch of salt to brighten the flavors.
Top with cake mix: Sprinkle the dry cake mix evenly over the fruit. Don’t mix it in—just make an even layer.
Add the butter: Drizzle the melted butter evenly across the dry cake mix.
Aim to moisten as much of the surface as possible.
Cook low and slow: Cover and cook on Low for 3.5 to 4.5 hours, or on High for 2 to 2.5 hours. The top should look set and slightly golden, with bubbly fruit around the edges.
Rest before serving: Turn off the heat and let it sit uncovered for 10–15 minutes. This helps the topping firm up slightly.
Serve warm: Spoon into bowls and add ice cream or whipped cream if you like.