In large bowl, combine flour, oats, sugar, baking soda and salt; cut in margarine until crumbly.
Reserving 1 1/2 cups of crumb mixture, press remainder on bottom of 13x9-inch baking pan. Bake 15 mins. Add nuts to reserved crumb mixture. In heave saucepan, over low heat, melt caramels with sweetened condensed milk, stirring until smooth. Spoon applefilling over prepared crust; top with caramel mixture then add reserved crumb mixture. Bake 20 mins or until set. Cool. Serve warm with ice cream or cool whip if desired
