01 - Combine rolled oats, milk, Greek yogurt, chia seeds, maple syrup, and vanilla extract in a medium bowl. Stir thoroughly until all ingredients are evenly incorporated.
02 - Whisk together cooled espresso, mascarpone cheese, cocoa powder, and maple syrup in a small bowl until smooth and creamy.
03 - Divide half of the oat mixture evenly between two jars or bowls, spooning it in to create the first layer.
04 - Spread half of the tiramisu mixture over the oat base in each jar, gently smoothing to create an even layer.
05 - Add remaining oat mixture on top of the tiramisu layer, then finish with the remaining tiramisu mixture.
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 with cocoa powder and sprinkle with dark chocolate shavings if desired.