Preheat the oven to 350°F and spray a 9x13-inch cake pan with cooking spray.
Prepare the cake by adding the cake mix, water, avocado oil, and eggs to a large mixing bowl. Whisk until smooth and well combined.
Transfer the batter to the prepared cake pan and bake according to package directions (about 25 minutes, or until a toothpick inserted in the center comes out clean).
Remove from the oven and allow to cool for 20 minutes. The cake should be warm but not hot — you should be able to touch the pan comfortably.
While the cake is cooling, whisk the strawberry Jello mix and hot water together in a spouted measuring pitcher until fully dissolved.
Using the handle of a wooden spoon or a chopstick, poke holes all over the top of the cake, about 1 inch apart. Push about three-quarters of the way through — don't go all the way to the bottom.
Slowly pour the Jello mixture all over the top of the cake, making sure it fills the holes evenly.
Let the cake sit at room temperature for 1 hour, then refrigerate for at least 2 hours (or overnight for best results).
Make the frosting: Add the softened cream cheese, powdered sugar, and vanilla extract to a large bowl. Using an electric hand mixer, beat until smooth and creamy. Gently fold in the Cool Whip until fully combined.
Spread the frosting evenly over the chilled cake. Top with sliced strawberries and serve.