PREHEAT oven to 375°F. Mix oats, graham crumbs, 1/3 cup each of the brown sugar and flour, the walnuts, butter and 1/2 tsp. of the cinnamon until well blended; set aside.
MIX 1/2 cup brown sugar, 2 Tbsp. flour and remaining 1/2 tsp. cinnamon in large bowl. Add apples; toss to coat. Place in 8-inch square baking dish; sprinkle with the oat topping.
BAKE 35 to 40 min. or until apples are tender. Cool slightly.