Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch pan with cooking spray.
Combine cake mix, 1 cup cold water, oil, and eggs in a large bowl. Beat together until batter is smooth. Spread the batter into the 9x13-inch pan.
Bake in preheated oven until a toothpick inserted into the center comes out clean, 34 to 38 minutes. Remove the cake from the oven. Cool slightly, about 5 minutes. Press down on hot cake with a piece of waxed paper or clean towel to flatten. Let cool completely, about 30 minutes.
Beat confectioners' sugar, cream cheese, and vanilla extract together in a bowl until smooth; blend in whipped topping. Spread mixture evenly across the cake.
Stir boiling water and gelatin together in a bowl until gelatin is completely dissolved, about 2 minutes; add 1 cup cold water. Pour over the cream cheese mixture. Let the gelatin sit until it begins to set, 5 to 7 minutes. Spread sliced strawberries on top.
Refrigerate until gelatin is completely set, about 1 hour.