Preheat the oven to 350 degrees. Prepare a 9X13 baking pan by lightly spraying with cooking spray and set aside.
In a large mixing bowl add cake mix, water, oil, eggs, and sour cream. Using a handheld mixer, beat on medium speed for 2 minutes, scraping the sides as needed.
Pour batter into the prepared baking pan. Place in the oven for 25-28 minutes. Check the cake after 25 minutes by inserting a toothpick into the center of the cake. If the toothpick does not come out clean add 2-3 additional minutes to the cooking time.
Allow the cake to cool for 5-10 minutes.
Using the end of a round spoon poke holes 1 inch apart throughout the cake. Let the cake cool completely.
In a medium size bowl add cold milk and instant pudding mix together and whisk for 2 minutes. Place in the refrigerator for 30 minutes to allow the pudding mixture to set up.
Once the cake is cool add the pudding to a piping bag. Pipe the lemon pudding into the holes that were poked into the cake.
Use an offset spatula to spread the remaining pudding evenly over the top of the cake.
Top with the thawed cool whip and spread over the whole cake using an offset spatula.
Cover and place in the refrigerator for at least 2 hours. When it is time to serve, add diced strawberries onto the top of the cake.