Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.
Pour both cans of peaches, including the juice, evenly into the prepared baking dish.
Sprinkle the dry yellow cake mix evenly over the peaches. Do not stir.
Drizzle the melted butter evenly over the cake mix, covering as much of the surface as possible.
Sprinkle with cinnamon and nutmeg, then add chopped pecans if using.
Bake for 45–50 minutes, or until the top is golden brown and the peach filling is bubbling around the edges.
Let the dump cake cool for about 10 minutes before serving.