Prepare cake per instructions on back of cake mix box for a 9x13 baking dish. Cool cake completely. Poke large holes throughout cake.
For Bakery Style Fluffy Cake - Substitute melted butter for the oil and milk for the water.
Whisk jello, boiling water and cold water in a large measuring cup. Pour into holes of cooled cake. Cover and refrigerate cake for 3 hours to overnight to set jello.
After jello is set, whisk together pudding and milk until a thick consistency is achieved. Fold in whipped topping until well blended.
Spoon pudding mixture onto cake, using a spatula to push pudding into holes. Smooth out evenly rest of pudding mixture on cake. Add slices of lemon for a garnish if desired. Keep refrigerated.
