Preheat your oven to 350°F. Line a 9×13-inch pan with aluminum foil and spray it with cooking spray to prevent sticking.
Prepare the cake mix according to the package instructions, which typically involves combining the mix with 3 egg whites, water, and oil. Mix until smooth and pour it into your prepared pan.
Bake the cake as directed on the package, usually around 23 to 28 minutes, until a toothpick inserted into the center comes out clean.
Once the cake is done, remove it from the oven and let it cool slightly. Using a fork, poke holes all over the top of the cake. This is essential as it allows the Jell-O mixture to seep in beautifully.
In a large microwave-safe measuring cup, add 1 cup of water and microwave it until boiling, which should take about 90 seconds on high power.
Add the strawberry Jell-O to the boiling water and whisk until it's fully dissolved, creating a vibrant mixture.
Next, add ½ cup of cold water to the dissolved Jell-O and whisk to combine. This addition helps it cool down and thickens the mixture.
Carefully pour the Jell-O mixture over the cake, ensuring it seeps into the holes you created. Take your time for an even distribution.
Cover the cake and refrigerate it for about 3 hours. This chilling time is essential for the flavors to meld and for the Jell-O to set.
After the chilling period, remove the cake from the fridge and spread the thawed whipped topping evenly over the surface.
Cover the cake again and refrigerate for at least another 2 hours, or overnight if possible. This ensures the cake is completely chilled and ready to serve.
When ready to serve, slice the cake, garnish with fresh strawberries, and enjoy the delightful combination of flavors!