In the bottom of a well seasoned cast iron skillet or Dutch oven, combine the frozen fruit, brown sugar, flour, and lemon zest. Stir to coat.
In a medium mixing bowl, stir together the cake mix, lemon lime soda, and lemon juice until just barely combined. Fold in the cubed butter and pour the mixture over the berries, covering them completely.
Preheat your grill to 375 degrees F and bake for 30-45 minutes, or until a toothpick inserted in the center comes out clean. Serve warm with whipped cream or ice cream.