In a very large mixing bowl, combine sugar, 1 tablespoon flour, cinnamon, and salt. Add apples and toss gently to coat. Spread apples in a 13x9x2-inch baking dish (3-quart rectangular).
In bowl, combine 1 cup flour, oats, brown sugar, baking powder, and baking soda. Sprinkle over the apple mixture. Drizzle melted butter evenly over all.
Bake, uncovered, in a 375 degree F oven 35 minutes or until bubbly and apples are tender. Cool 30 minutes and spoon into dessert dishes. Serve with vanilla ice cream, if you like.