Combine the graham cracker crumbs and melted butter in a small bowl.
Divide the mixture evenly between 6 dessert bowls or dishes (stemless wine glasses work nicely for desserts like this) and press the crumbs down into the bottom of the dishes.
In a large bowl mix the room temperature cream cheese together with the powdered sugar until it's light and fluffy and smooth. I'd suggest using a hand mixer or a stand mixer for this, on medium to medium-low speed.
Add the lemon zest and juice and mix on medium speed until combined.
Add the whipped cream or whipped topping and gently fold it in with a rubber spatula just until everything is combined.
Add the cheesecake mixture to a piping bag fitted with a large open tip (or no tip at all - simply cut the end off a disposable piping bag to create a large opening). Swirl the cheesecake filling into each of the 6 prepared cups on top of the crumb mixture. Be sure to divide the filling evenly among the 6 cups.
Place the cups in the fridge to chill for about 2 hours.
Before serving, add a dollop of whipped cream and a lemon slice on top of each cup.
These cheesecake cups can be made one day ahead of time and stored in the fridge until ready to serve.