Prep the pan. Lightly grease a 9-inch pie dish or line the bottom with parchment for easier slicing.
Make the crust. In a bowl, combine crushed crackers, melted coconut oil or butter, sweetener (if using), and a pinch of salt.
Stir until the crumbs are evenly moistened and hold together when pressed.
Press and chill. Firmly press the crust mixture into the bottom and up the sides of the pie dish. Use the bottom of a measuring cup for a tight, even layer. Chill in the fridge for 15–20 minutes while you make the filling.
Whip the base. In a large bowl, beat the cream cheese with an electric mixer until smooth, about 1 minute.
Add peanut butter and beat until fully combined and fluffy.
Blend in the protein. Add the protein powder, powdered sugar, vanilla, and salt. Mix on low at first to avoid a powder cloud, then increase speed until smooth.
Lighten it up. Add the Greek yogurt and beat just until creamy. If the mixture seems too thick to spread, add milk 1 tablespoon at a time until silky and spreadable.
Fill the crust. Spoon the filling into the chilled crust and smooth the top with a spatula.
Chill to set. Refrigerate for at least 4 hours, or overnight for a cleaner slice.
The filling will firm up as it chills.
Finish and serve. Top with chocolate shavings, crushed peanuts, or a drizzle just before serving. Slice with a sharp knife, wiping between cuts for neat edges.