Preheat the oven to 350 degrees F. Grease a 12-inch oven-safe skillet or a 9x13 baking dish with non-stick cooking spray.
Add the blueberries to the prepared dish and drizzle with lemon juice. Dump the dry cake mix onto the blueberries, and shake the pan to evenly distribute it. Pour the melted butter all over the top.
Bake for 35-45 minutes, or until golden brown.
Remove from the oven and serve warm with vanilla ice cream, if desired.