Prepare the grill for indirect heat, preheat to medium (350 degrees).
Line a cast iron Dutch oven with heavy duty aluminum foil. Place the cherry pie filling and pineapple, along with the juices, in the Dutch oven. Stir to combine. Sprinkle the cake mix evenly over the top. Dot the butter all over the top of the cake mix. Sprinkle the pecans over. Put the lid on the Dutch oven and cook on the grill, with the lid closed and maintaining a temperature of about 350 degrees, for 55–65 minutes or until the cake topping is cooked through.