In a microwavable mug (make sure that it has a 1-cup capacity, ~250 mL, and is microwave-safe), stir together with a fork the flour, crushed Oreo cookies, brown sugar, baking powder, and salt.
Measure the milk, oil and vanilla directly into the mug. Stir again until there are virtually no more lumps. Make sure to scrape the bottom edges to make sure there are no flour pockets!
Place the mug in the microwave, and cook on high for 90 seconds. The cake will puff up as it cooks. Use a cake tester and insert it into the centre of the cake to test if it's done cooking.
Carefully take the mug out of the microwave (it’s hot!) and let the cake sit for a couple of minutes before diving in with spoon. You can also top it with sweetened whipped cream or ice cream, and more crushed Oreo cookies.