Prepare and bake the cake according to package directions in a greased 9x13-inch pan.
Remove from the oven and poke all over with a fork, skewer, or back of a utensil.
Whisk together the sweetened condensed milk and RumChata in a large measuring cup and pour all over the top of the cake. Allow the cake to cool and soak at room temperature for 2 hours.
Spread thawed whipped topping all over the top of the cake.
Combine the cinnamon and sugar in a small bowl and sprinkle over the top of the cake.
Notes
Nutrition calculated with a similar cream based liquor.