For the crust, in a mixing bowl cream margarine and brown sugar until fluffy. Add flour, oats, salt, and baking powder. Mix well. Stir in nuts if you want. Set aside 2 cups of this mixture, then press the remaining mixture into the bottom of an ungreased 9-x13-inch pan. For filling, toss apples with flour and spoon over crust. In a sauce pan, melt the caramels and margarine over low heat. Watch so they do not burn. Drizzle caramel mixture over apples. Top with reserved oat mixture. Bake at 400 degrees for 25–30 minutes until lightly browned. Cool before cutting into bars. Makes about 15–20 servings. Good served with a scoop of vanilla ice cream.