HEAT oven to 350 degrees F. Combine flour, oats, brown sugar, cinnamon, baking soda, salt and nutmeg in large bowl. Cut in butter with pastry blender or two knives until mixture resembles coarse crumbs. Reserve 1 3/4 cups crumb mixture; press remaining crumb mixture onto bottom of an ungreased 13 x 9-inch baking pan. Bake 15 minutes.
ARRANGE apples over partially baked crust. Mix sweetened condensed milk and 1/2 cup caramel topping until blended. Pour evenly over apples. Add walnuts to reserved crumb mixture; sprinkle over apple layer.
BAKE 45 to 50 minutes or until apples are tender. Cool in pan on wire rack. Serve warm topped with vanilla ice cream and remaining caramel topping.