Preheat oven to 350F and line a muffin pan with cupcake liners.
Whisk together flour, baking powder, and salt in a bowl.
In a separate bowl, blend together egg, oil, sugar, lemon juice, and lemon zest.
Blend the wet mixture into the dry ingredients.
Stir the milk in just until batter is smooth.
Divide the batter into the muffin pan and bake for 20-25 minutes.
Meanwhile, blend together ingredients for the frosting.
Take muffins out of the oven and leave to cool.
Top with frosting.