Preheat your oven according to the cake mix instructions.
Prepare and bake the cake in a 9x13 inch pan as directed. Let it cool for 15 minutes.
Using the handle of a wooden spoon, poke holes all over the cake.
In a bowl, dissolve the strawberry Jell-O in boiling water. Stir in cold water.
Slowly pour the Jell-O mixture evenly over the cake, letting it soak into the holes.
Refrigerate the cake for at least 2 hours to set.
Spread the whipped topping evenly over the chilled cake.
Garnish with fresh sliced strawberries before serving.