Prepare the cake mix according to box instructions, replacing the water for peach juice. Grease and bake in a 9x13 inch baking dish. Set aside to cool while making the filling.
For the peach filling
Add the chopped peaches to a food processor and pulse until pureed but still slightly chunky. Pour into a small saucepan along with the sugar and lemon juice. Cook over medium-high heat and bring to a boil. Simmer for 3-4 minutes or before it begins to thicken.
Use the end of a wooden spoon to poke holes all over the cake.
Pour the peach sauce over the cake and make sure all the holes are filled.
For the topping
Beat the cream cheese and sugar until smooth and creamy. Fold in the cool whip until combined. Spread over the cake in an even layer. Refrigerate for at least 30 minutes or until cooled and set. Slice, garnish with peach slices and mint, and enjoy.