Preheat oven to 350° F. Place the sliced apples in a 9 x 13 x 2-inch pan.
Mix the sugar, 1 Tbsp flour and ground cinnamon together and sprinkle over apples. Pour the water evenly over all.
Combine the oats, flour, brown sugar, baking powder, baking soda and melted butter together. Crumble evenly over the apple mixture.
Bake for about 45 minutes. Serve warm with a scoop of vanilla ice cream, if desired.Servings: 12