01 - Combine rolled oats, milk, Greek yogurt, chia seeds, maple syrup or honey, and vanilla extract in a medium bowl. Stir thoroughly until all ingredients are well incorporated.
02 - Whisk together cooled espresso, mascarpone cheese, cocoa powder, and maple syrup or honey in a small bowl until completely smooth and creamy.
03 - Divide oat mixture evenly between two serving jars or bowls, spooning half of the mixture into each container.
04 - Spread half of the tiramisu mixture over the oats in each jar, using a spoon to gently distribute it evenly.
05 - Spoon remaining oat mixture on top of the tiramisu layer, then finish with the remaining tiramisu mixture spread over the oats.
06 - Cover jars or bowls tightly with lids and refrigerate for at least 8 hours or overnight to allow flavors to meld and oats to soften.
07 - Before serving, dust the top generously with cocoa powder and sprinkle with dark chocolate shavings if desired.