Preheat oven to 325°F (160°C).
In a mixing bowl, whisk Greek yogurt until smooth.
Add eggs one at a time, mixing well after each addition.
Stir in corn starch, erythritol, vanilla extract, and lemon zest if using.
Pour batter into a lined or greased 8-inch springform pan.
Bake for 35–40 minutes until edges are set and center is slightly jiggly.
Let cool to room temperature, then refrigerate for at least 4 hours or overnight before serving.