Mixing the cake batter: Preheat oven to 350 degrees F. In a bowl blend together starter, water, Gentle Sweet, egg, egg whites, pineapples, and vanilla together. Set aside. In separate bowl combine carrots, flour, cinnamon, salt, baking powder, and baking soda together. Mix the wet and dry ingredients together just until mixed. Pour batter into a 9 x 13 baking pan. Mixing the topping: Chop walnuts. Mix walnut pieces, sweetener, oats, and butter together until combined. Sprinkle over cake batter. Bake for 35-45 minutes or into a toothpick inserted in the center comes out clean.