Preheat oven for 350. In 13x9 baking dish pour melted and slightly cooled margarine. (I also sprayed the sides with butter flavored cooking spray.) Sprinkle splenda brown evenly over bottom and mix with the margarine to dissolve. Arrange pineapple slices. Mix cake mix and remaining ingredients together.( The batter will be thick.) Pour or spoon bater evenly over pineapple and mixture.Place in preheated oven and bake for about 25-29 minutes or until toothpick inserted in center comes out clean. Turn out onto serving tray to cool.