Combine the hot water and the gelatin and whisk until well combined. Set aside.
In a separate bowl, whisk together cream cheese, sugar and vanilla until smooth and creamy. Set aside.
Add orange juice to the gelatin mixture and whisk to combine.
In a large bowl, combine the orange juice/gelatin mixture with the cream cheese mixture and whisk until smooth.
Add in the Cool Whip and 1 can of the mandarin oranges. Mix using a rubber scraper until everything is combined.
Pour mixture into the graham cracker crust. Refrigerate for about 4 hours, until solid. (If you want to speed up this process, feel free to put it in the freezer. Just defrost it prior to serving.
Garnish with remaining mandarin oranges.