Mix strawberries, sugar and vanilla. Spoon 1/2 of the strawberries on 1 cake layer. Drizzle with 1/2 the chocolate glaze; top with 1/2 the whipped topping. Repeat layers. Garnish with chocolate-dipped strawberries, if desired. Refrigerate.
To prepare chocolate glaze, microwave chocolate, water and margarine in large microwavable bowl on HIGH 1 to 2 minutes until chocolate is almost melted, stirring once. Remove from microwave and stir until chocolate is completely melted. Stir in sugar and vanilla until smooth. For thinner glaze, add 1/2 to 1 teaspoon additional water.
NOTE: Recipe time does not include baking the chocolate cake mix.