Preheat oven to 325°F. Line an 8-inch springform pan with parchment and lightly grease.
Mix almond flour, butter, and erythritol; press evenly into the bottom of the pan. Bake for 8 minutes, then let cool.
In a large bowl, beat cream cheese, Greek yogurt, whey protein, and sweetener until smooth.
Add eggs one at a time, then stir in heavy cream, vanilla, and lemon zest.
Pour the mixture over the crust, smooth the top, and bake for 35–40 minutes until set but slightly jiggly in the center.
Let cool completely, then refrigerate for at least 4 hours before slicing.