- In a microwave-safe mug, combine the flour, granulated sugar, baking powder, and salt. Mix well. 
- Add the milk, vegetable oil, and vanilla extract to the dry ingredients. Stir until just combined. 
- In a small bowl, mix together the brown sugar and ground cinnamon. Drizzle the melted butter over the batter in the mug, then sprinkle the cinnamon-sugar mixture on top. Use a fork or toothpick to swirl the filling into the batter. 
- Microwave the mug on high for 1 minute and 30 seconds, or until the center is set. Cooking time may vary based on your microwave's wattage. 
- While the cinnamon roll is cooling, prepare the icing by whisking together the powdered sugar, milk, and vanilla extract until smooth. 
- Drizzle the icing over the warm cinnamon roll and enjoy!