Peel, core and chop apples into bite-sized pieces. In bowl, mix apples with brown sugar, cinnamon and flour, if desired, which helps keep apples from sinking to bottom. Set aside.
In large mixing bowl, mix spice cake mix, butter, eggs and milk. Mix in apples and pour into 9-by-13-inch pan. Bake 30-35 minutes, or until toothpick inserted in center comes out clean.
Let cool then mix powdered sugar and milk; pour over cooled cake. Top with pecans.