Crush the cookies: Place Oreos in a zip-top bag and crush with a rolling pin until you have a mix of fine crumbs and small chunks.
Set aside a tablespoon for garnish.
Blend the base: In a bowl, whisk the Greek yogurt, protein powder, cocoa (if using), sweetener, vanilla, and salt. Add 1/3 cup milk to start. Whisk until smooth and creamy.
If it’s too thick, add more milk 1 tablespoon at a time.
Optional thickener: If you like a denser pudding, whisk in the instant pudding mix. It will firm up more as it chills.
Fold in Oreos: Stir in most of the crushed Oreos, leaving some for topping. Don’t overmix—you want bits of cookie throughout.
Chill: Spoon into jars or bowls.
Cover and refrigerate for at least 30 minutes, or up to 24 hours for the thickest texture.
Top and serve: Before serving, add a dollop of whipped cream, a sprinkle of cookie crumbs, and any extra toppings you like.