Heat oven to 200ºC . Grease square pan, sugar and egg; beat vigorously 30 seconds. Spread half of the batter in pan. Arrange apple slices on batter; sprinkle with half of the Streusel Topping. Spread remaining batter over apple slices; sprinkle with remaining topping. Sprinkle with nuts. Bake until wooden pick inserted in center comes out clean, about 25 minutes; cool. Drizzle with glaze.
Streusel Topping: Mix baking mix, brown sugar, cinnamon and nutmeg, cut in margarine until crumbly. Glaze: Mix powdered sugar and milk until smooth and of desired consistency. Makes 8 servings.