Add the blueberries to a large bowl, along with the lemon juice and brown sugar. Stir well to dissolve the brown sugar.
Grease a large baking dish with non-stick spray. Add in the blueberry mixture, then evenly sprinkle the cake mix over the blueberries. Top with slices of butter.
Bake for 35-45 minutes, or until the cake is golden and everything is bubbly. Serve warm with vanilla ice cream and enjoy!