In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted butter, mixing until well blended. Press this mixture firmly into the bottom of individual serving cups, ensuring an even layer.

In a large mixing bowl, beat softened cream cheese with a hand mixer until smooth and creamy, about 2 minutes on medium speed. Gradually add powdered sugar, mixing well after each addition.

Mix in key lime juice and lime zest until fully incorporated, creating a tangy filling.

Gently fold whipped topping into the cream cheese mixture using a spatula, being careful to maintain the mixture's lightness.

Spoon the cream cheese filling over the prepared crusts in each cup, smoothing the tops. Cover each cup with plastic wrap and refrigerate for at least 2 hours.

Once set, uncover and add a dollop of whipped topping on each cup. Sprinkle with additional lime zest and serve chilled.