To a large bowl, add the milk, Greek yogurt, mascarpone cheese, maple syrup, vanilla extract, & espresso powder or instant coffee. Whisk to combine well. Add the oats & chia seeds & stir well to combine.
To a second large bowl, add the heavy cream, mascarpone cheese, Greek yogurt, maple syrup, & vanilla extract. Whisk to combine well, breaking down the yogurt & mascarpone cheese a bit. Fit a hand mixer with the whisk attachment, then whip on medium-high speed until medium peaks form, 3-4 minutes.
Transfer the overnight oats & mascarpone whipped cream to separate airtight containers. Cover & set in the refrigerator to chill until the oats have absorbed most of the liquid & are tender enough to chew easily, at least 2 hours or up to overnight.
To serve, transfer ¼ of the tiramisu overnight oats mixture (approx. 1 cup) to a small glass or jar. Spread ¼ of the mascarpone whipped cream mixture (approx. 2-3 tablespoons) over top. Finish with a light dusting of cocoa powder. Enjoy!