In a medium-sized bowl or a wide-mouth mason jar, combine the rolled oats, protein powder, and a pinch of salt. Whisk these dry ingredients together to ensure the protein powder is evenly distributed and won’t clump when liquid is added.
Pour the chilled espresso and the almond milk into the oat mixture. Add the vanilla extract and half of the optional sweetener if you prefer a sweeter base. Stir everything thoroughly until the oats are completely submerged and the protein powder has dissolved into a smooth liquid.
In a separate small bowl, mix the Greek yogurt with the remaining sweetener. Stir it until it is smooth and creamy. This layer acts as the “mascarpone” element of the tiramisu, providing a tangy and thick contrast to the coffee-soaked oats.
If you mixed the oats in a bowl, transfer them to a glass jar. Smooth the top with a spoon, then spread the yogurt mixture evenly over the oats. Seal the jar with a lid and place it in the refrigerator for at least 4 hours, or ideally overnight, to allow the oats to soften.
Just before serving, use a small sieve to dust the top of the yogurt layer with a generous coating of unsweetened cocoa powder. This adds the signature tiramisu look and a deep chocolate aroma that hits you as soon as you open the jar.