From the cookbook Mug Meals by Dina Cheney.
Spray the inside of a 12-oz. mug with cooking spray. Stir together all of the ingredients in a small to medium bowl, then pour into the mug.
Cover and microwave until the oats are cooked, about 3 minutes.
Pour the hot mixture onto a piece of parchment or waxed paper, shaping into a rectangle or narrow traditional bar. Chill until cold and solid, 30 minutes or more.