Preheat the oven: Set the oven to 350°F (175°C) and line a jumbo (or regular) cupcake pan with cupcake liners.
Make the cake batter: In a mixer, combine the cake mix, guava juice, eggs, and coconut oil. Mix on low for 30 seconds, then scrape the bowl. Mix again on medium speed for 2 minutes.
Divide and bake: Fill the cupcake liners up to ⅓ full with the batter. Bake for 19-22 minutes, or until the tops are light golden. Once done, transfer the cupcakes to a wire rack to cool completely.
Prepare the guava gel topping: In a medium saucepan, bring the guava juice and sugar to a boil over medium heat. Make a slurry by whisking together the cornstarch and water. Remove the guava juice from heat and whisk in the cornstarch slurry. Return to the heat and bring the mixture back to a boil for one minute. Let the gel cool in the refrigerator.
Make the cream cheese layer: Beat the softened cream cheese until fluffy. Add sugar and vanilla extract, mixing well. Slowly fold in the thawed Cool Whip, and refrigerate the mixture until ready to use.
Assemble the cakes: Once the cupcakes are completely cool, spread the cream cheese mixture evenly over the tops. Refrigerate until the cream cheese layer is set.
Finish with the guava gel: Glaze the tops of the cupcakes with the cooled guava gel. Refrigerate until ready to serve for the perfect tropical treat!