Heat oven to 400 degrees. Grease 9 square pan. Mix baking mix, 2/3 cup milk, egg and white sugar; beat vigorously 30 seconds. Spread in pan. Mix walnuts, brown sugar, cinnamon and nutmeg in small bowl; sprinkle over batter. Spoon applesauce over walnut mixture. Bake until wooden pick inserted in center comes out clean, about 25 minutes. Cool 30 minutes. Meanwhile, heat 2 Tbsp. margarine in 1 quart saucepan over low heat until golden brown; remove from heat. Mix in powdered sugar and vanilla. Stir in mix until smooth and of desired consistency. Drizzle over coffee cake.