In a medium bowl, whisk together the oat flour, protein powder, and baking powder.
In a separate bowl, whisk the egg whites, 1/2 cup Greek yogurt, cooled espresso, and vanilla extract until smooth.
Gradually fold the wet ingredients into the dry ingredients until just combined; allow the batter to rest for 5 minutes to thicken.
Heat a non-stick skillet over medium-low heat and lightly coat with cooking spray.
Portion 1/4 cup of batter per pancake onto the skillet; cook until bubbles form on the surface, then flip and cook for another 90 seconds.
In a small bowl, mix the mascarpone or yogurt with maple syrup to create the cream filling.
Stack the pancakes, spreading a layer of the cream mixture between each pancake.
Finish the stack by dusting the top generously with unsweetened cocoa powder.