In a microwave-safe mug or bowl, whisk together the flour, sugar, cocoa powder, baking powder, and salt until well combined.
Add the milk, vegetable oil, and vanilla extract to the dry ingredients and mix until smooth and no lumps remain.
Stir in the chocolate chips evenly throughout the batter.
Microwave on high for 60 seconds. The muffin should rise and be set but still moist. If needed, microwave in additional 10-second increments until cooked through but avoid overcooking.
Allow the muffin to cool for 1-2 minutes before eating. Enjoy directly from the mug or transfer to a plate.