Whisk the base: In a medium bowl or mason jar, whisk milk, Greek yogurt, protein powder, cocoa, hazelnut butter, vanilla, sweetener, and salt until smooth.
Break up any cocoa or protein clumps with the back of a spoon if needed.
Add chia seeds: Stir in the chia seeds until they’re evenly distributed. Let the mixture sit for 5 minutes, then stir again to prevent clumping at the bottom.
Chill to thicken: Cover and refrigerate for at least 3 hours, ideally overnight. The chia seeds will swell and create a pudding-like texture.
Adjust consistency: In the morning, give it a thorough stir.
If it’s too thick, add a splash of milk. If it’s runny, stir in 1–2 teaspoons more chia seeds and rest 15–20 minutes.
Add toppings: Finish with sliced banana, chopped hazelnuts, or a sprinkle of chocolate. Serve cold.