01 - Combine graham cracker crumbs and granulated sugar in a mixing bowl. Pour in melted butter and stir until fully incorporated and mixture resembles wet sand. Press firmly into bottom and up sides of a 9-inch pie dish. Refrigerate for 30 minutes to set.
02 - Blend seedless watermelon in blender until completely smooth. For a silkier texture, strain through fine-mesh sieve to remove excess pulp. Set aside.
03 - Sprinkle gelatin packet over cold water in small saucepan. Let stand for 5 minutes to bloom. Place over low heat, stirring constantly until gelatin dissolves completely. Do not boil. Remove from heat.
04 - Whisk together watermelon puree, sugar, and lemon juice in large bowl. Stir in dissolved gelatin mixture until well combined. Let mixture cool to room temperature, about 10-15 minutes.
05 - Gently fold whipped topping or whipped cream into watermelon mixture using spatula until fully incorporated and smooth. Take care not to deflate the mixture.
06 - Pour filling into chilled crust. Smooth top with spatula or offset spatula. Refrigerate for minimum 4 hours or overnight until completely set.
07 - Top with additional whipped cream, fresh watermelon balls or slices, and mint leaves before serving. Slice into wedges and serve chilled.