01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with cooking spray or butter. Prepare the cake batter according to package instructions, typically combining the mix with eggs, oil, and water. Pour batter into the prepared dish and bake for the time specified on the box, usually 25-30 minutes, until a toothpick inserted comes out clean. Allow the cake to cool for 20 minutes.
02 - Using the tines of a fork or the handle of a wooden spoon, poke holes evenly across the entire surface of the cooled cake. Press down gently to create channels that reach nearly to the bottom of the pan, spacing them about 1 inch apart for optimal gelatin distribution.
03 - Pour 1 cup of boiling water into a medium heat-safe bowl. Add the strawberry gelatin powder and whisk vigorously for 2 minutes until completely dissolved. Stir in 1/2 cup of cold water and mix well. The mixture should be clear and slightly thickened.
04 - Slowly pour the liquid gelatin mixture evenly over the surface of the poked cake. Work systematically from one end to the other, ensuring the gelatin seeps into the holes and permeates the cake structure. Allow the cake to sit for 5 minutes to absorb the liquid.
05 - Transfer the baking dish to the refrigerator and chill for at least 2 hours, or until the gelatin is completely firm and set. The cake can be refrigerated for up to 24 hours before adding the final topping.
06 - Remove the chilled cake from the refrigerator. Spread the whipped topping evenly over the entire surface using a spatula, creating smooth, decorative swirls if desired. Arrange fresh strawberry slices in an attractive pattern on top. Add fresh mint leaves as a finishing garnish for color contrast. Cut into 12 equal squares and serve immediately, or return to refrigerator until serving time.