From the cookbook Mug Meals by Dina Cheney.
Spray the inside of a 16-oz. mug with cooking spray.
In a small bowl, use a fork to whisk together ¼ cup of the flour, the oats, baking powder, cinnamon, and salt.
Whisk together the milk, oil, egg, honey, and vanilla in a small bowl. Pour the dry ingredients into the wet and mix just until combined.
In a small bowl, toss the berries with the remaining ½ tsp. flour and add to the batter. Mix just until combined. Pour into the mug.
Cover and microwave until just cooked through in the center, about 2½ minutes (do not overcook).