Heat oven to 375°F In small saucepan, combine caramels and half-and-half; cook over low heat, stirring occasionally, until caramels are melted. Keep warm.
Lightly spoon flour into measuring cup; level off. In large bowl, combine 2 1/2 cups flour, 1/4 cup sugar and salt. With pastry blender or fork, cut in margarine until mixture resembles coarse crumbs. Add oil, water and egg; mix well. Press crust mixture evenly in bottom and up sides of ungreased 15x10x1-inch baking pan.
In large bowl, combine all apple filling ingredients; toss lightly. Spoon into crust-lined pan. Drizzle warm caramel sauce over apples.
In small bowl, combine all topping ingredients except nuts; beat until smooth. Spoon over apples, spreading slightly. Sprinkle with nuts.
Bake at 375°F for 35 to 45 minutes or until light golden brown. Cool. Cut into squares. Store in refrigerator.