Drain the canned peaches and reserve the juice. Spread the drained peaches evenly into the prepared dish.
Measure ½ a cup of the reserved juice.
Place the cornstarch in a small bowl, and mix in about 1 - 2 tablespoons of the measured ½ cup of juice, then mix to a smooth paste, add the remaining juice and mix in the brown sugar.
Pour the juice, cornstarch, and sugar mixture over the peaches.
Sprinkle the dry cake mix evenly over the peaches. Spread it out to cover as much of the surface as possible.
Drizzle the melted butter over the cake mix layer, covering as much of the dry mix as possible.
Optional, sprinkle a little ground cinnamon on top for added flavor.
Place the baking dish in the preheated oven and bake for 35-40 minutes, or until the top is golden brown and the filling is bubbly around the edges.
Remove from the oven and let it cool for a few minutes before serving.
Serve with fresh whipped cream, custard or ice cream.