In the mug sprayed with nonstick cooking spray, combine flour, baking powder and salt. Using a fork, beat in egg, sugar, oil, lemon zest and lemon juice until very well blended.
Microwave on High for 1 1/2 to 2 minutes (checking at 1 1/2) or until risen and center is just set. Let cool slightly or entirely in mug. Eat directly from mug or gently remove to a small plate.
Icing:
In a small bowl or cup, use a fork to stir confectioners’ sugar and lemon juice until smooth. Drizzle over cake.
Notes
Using oil, instead of butter, in this recipe helps to keep the cake extra-moist.
You can use 1/8 tsp (0.5 mL) lemon extract in place of the lemon zest.