Lightly grease a large microwave safe mug that holds at least 12 oz. In a small bowl, stir together the coconut sugar, cinnamon and melted butter for the swirl until it forms a thick paste.
In the mug, whisk the egg, almond milk, maple syrup, melted butter and vanilla with a fork until smooth.
Add the protein powder, flour, baking powder and salt and whisk until you have a thick, smooth batter with no dry spots at the bottom of the mug.
Dollop the cinnamon paste over the batter and drag a toothpick through it in a spiral, like the swirl of a cinnamon roll.
Microwave for 60 seconds, then check. If the center still looks wet, continue in 10-second bursts until the top is puffed and just set, usually 70 to 80 seconds total.Protein cakes turn rubbery when overcooked, so pull it as soon as the top springs back. Let it rest for 1 minute.
Stir the cream cheese, powdered sugar, protein powder and almond milk until smooth, then spread over the warm cake so it melts into the swirl. Enjoy right away while warm and gooey.