In a jar or bowl, combine oats, milk, chia or flax, sweetener, vanilla, and salt.
Stir well to fully moisten the oats.
Fold in the Greek yogurt if using. This makes the oats extra creamy and adds protein.
Warm the Nutella for 10–15 seconds in the microwave to loosen it. Spoon it over the oat mixture.
Use a butter knife or spoon to gently swirl the Nutella through the oats.
Don’t overmix—you want visible ribbons.
Cover and refrigerate for at least 4 hours, ideally overnight, until thick and pudding-like.
In the morning, give it a quick stir. Add a splash of milk if it’s too thick. Top with banana slices, berries, or chopped hazelnuts, and enjoy.