Make the tart: Preheat the oven to 325 degrees F.
Whisk the eggs and yogurt together in a bowl, then whisk the sugar, lemon zest, and lemon juice into the bowl until the sugar starts to dissolve and is fully blended.
Pour the lemon filling into the graham cracker crust and bake for 25-30 minutes until the filling has just set. It should still jiggle slightly in the center, but will no longer be liquid.
Cool to room temperature, then cover with foil and refrigerate.
To serve: Bring to room temperature and top with whipped cream for serving, if desired.