Prepare and bake cake as directed on the back of the box for a 9 x13-inch pan.
Let the cake cool for 20 minutes. "Poke" the cake with the end of a small wood spoon or large fork. Space pokes about 1/2-inch apart, until the entire surface of the cake is covered with holes.
In a medium bowl, whisk together Jello and boiling water, until the Jello is completely dissolved. Whisk in cold water, until well combined. Slowly pour Jello over the cake filling the holes. Cover the cake with plastic wrap and refrigerate for three hours.
In a large bowl, using an electric mixer, beat softened cream cheese, confectioners' sugar, and vanilla until smooth. Add Cool Whip, beat on low, until just combined. Spread on top of cake.
Top with fresh strawberries. Keep refrigerated until ready to serve.
This recipe can easily be made with raspberry Jello and fresh raspberries, in place of Strawberry Jello and fresh strawberries if desired.