PREHEAT oven to 350°F. LINE 13x9x2-inch baking dish with Reynolds Wrap Non-Stick Foil with the non-stick (dull) side facing up towards the food and the shiny side facing the dish; set aside.
ARRANGE apples evenly in dish. Sprinkle with cinnamon and sugar; set aside.
MIX flour, oats, brown sugar, walnuts and salt in a medium bowl. Cut in butter until well blended. SPRINKLE flour mixture over apples.
BAKE 40 to 45 minutes, until apples are soft and topping is lightly browned. SERVE warm with ice cream.