In a microwave-safe mug, combine the flour, baking powder, baking soda, and salt. Give these dry ingredients a good stir to mix them well.
Add the milk and olive oil to the mug. Use a fork or a small whisk to mix everything until a smooth dough forms, making sure there are no dry flour bits hiding in the corners.
Carefully spoon the tomato pizza sauce over the dough, spreading it gently. Then, generously sprinkle the shredded mozzarella cheese and a little dried oregano on top.
Microwave on high for 1 minute.
Carefully remove the mug from the microwave (it will be hot!). If using, arrange your sliced pepperoni (or veggie toppings) on top of the melted cheese.
Return to the microwave and cook for another 10-20 seconds, or until the cheese is bubbly and the edges look set.
Let your mug pizza cool for a few minutes before eating, as it will be very hot! Enjoy your super speedy, healthy-ish pizza!