Preheat the oven to 350°F. Grease a 9x13-inch cake pan and set aside.

Mix the batter: In the bowl of a hand or stand mixer, combine the cake mix, sour cream, water, melted butter, and eggs. Beat on low speed for about 30 seconds or until just combined. Scrape the sides of the bowl. Then beat on medium speed for 1 to 2 minutes more. Pour the batter into the prepared pan.

Bake for 30 to 33 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.

Make the topping: In a clean mixing bowl with a whisk attachment, beat the heavy cream, powdered sugar, and lemon juice on high speed until stiff peaks form (about 2 to 3 minutes). Stir in the lemon zest by hand until fully mixed. Keep the topping in the refrigerator until you're ready to use it.

Frost and garnish: Spread the whipped lemon cream evenly over the cooled cake. Top with fresh strawberries and lemon slices. Serve chilled or at room temperature.