Make the batter: In a large microwave-safe mug, whisk almond flour, ground coconut, baking powder, sweetener, and salt. Stir in egg, melted butter, and vanilla until smooth.
Microwave to rise: Cook on High 70–80 sec until top is set and springs back.
Mix tres leches soak: In a small bowl whisk heavy cream, coconut milk, almond milk, and the ½ tsp sweetener.
Soak & chill: Poke the warm cake 6–8 times with a skewer. Pour milk mix slowly over the top. Let stand 2 min to absorb, or refrigerate 15 min for a cool version.
Serve: Top with a spoonful of whipped cream and a dusting of cinnamon.