Get a microwave-safe mug that can hold 10-12 ounces.
Add milk and Oreo cookies to the mug. Use a fork to crush the Oreos until they become a paste.
Add oil, vanilla, and sugar. Use the fork to mix everything together.
Sift in flour, cocoa powder, baking powder, and salt. Gently mix with the fork until just combined, without overmixing.
Microwave the mixture on high for 60-90 seconds, until the cake is fully cooked (takes around 1 minute and 25 seconds).
While the cake is still warm, sprinkle chocolate chips on top so they melt. Spread the melted chocolate over the cake.
Top the cake with crushed Oreo cookies.
Serve and enjoy your Oreo mugcake!