Move oven rack to middle position and preheat oven to 350 degrees F. Lightly grease a 9x13-inch baking dish with nonstick cooking spray.
In a large bowl toss together thawed and drained peaches, brown sugar, cornstarch, lemon juice, and cinnamon.
Pour the peaches into the prepared baking dish and smooth into an even layer.
Sprinkle the cake mix over the peaches.
Place the butter pieces over the cake mix, spacing them out evenly.
Bake until the peaches are bubbling and the top is golden brown, about 40-45 minutes, rotating halfway through baking.
In the last 15 minutes of baking, you will want to peek at the cobbler to see any dry spots where the butter hasn't mixed in with the cake mix. If there are dry spots, use a spoon to give the dry spots a quick mix.
COOL AND SERVE:
Transfer the cobbler to a wire rack to cool for 10 minutes because serving. Serve with a scoop of vanilla ice cream (optional).
You can use 2 pounds of fresh peaches or 2 large cans of drained peaches.