In a large bowl or jar, combine oats, milk, Greek yogurt, chia seeds, maple syrup (or honey), and espresso powder. Stir well until thoroughly mixed.

Cover and refrigerate for at least 5 hours, ideally overnight, to allow the oats to soak and soften.

In a separate bowl, whisk together additional Greek yogurt, maple syrup, and optional protein powder for a yogurt layer.

Layer the oat mixture and yogurt in a glass or jar, starting with half of the oat mixture followed by half of the yogurt mixture.

Dust the top lightly with cocoa powder using a fine-mesh sieve.

Serve chilled, optionally allowing the layers to meld for an additional half hour.