Weight Watchers Banana Muffins with Tart Lemon Icing

A friend recently started Weight Watchers, so I'm making her these muffins. They're only 3 points!

POINTS® Value: 3 Servings: 18 Preparation Time: 15 min Cooking Time: 30 min Level of Difficulty: Easy

If you like muffins, then you must try these. They're like mini-frosted banana cakes with a surprising burst of lemon.

Ingredients
1/2 cup(s) sugar
5 tbsp unsalted butter, softened
1 large egg(s)
1 tsp vanilla extract
2 cup(s) all-purpose flour
2 tsp baking powder
1 tsp baking soda
1/4 cup(s) fat-free skim milk
4 large banana(s), ripe, mashedIcing
1 cup(s) powdered sugar
1 tbsp unsalted butter, softened
1 tbsp fresh lemon juice
1 tsp lemon zest, strips, or more to taste
1 tsp vanilla extract
Instructions
Preheat oven to 350ºF. Line 18 muffin holes with paper liners.
Place sugar and butter in a large bowl; cream with an electric mixer until light and fluffy. Add egg and vanilla; beat until thoroughly mixed.
In another large bowl, mix together flour, baking powder and baking soda. Add half of flour mixture to butter mixture; beat well with mixer. Add milk and remaining flour mixture; beat until batter is combined and then fold in mashed bananas.
Spoon batter into muffin liners about 3/4 full. Bake until muffins start to brown and a tester inserted in center of a muffin comes out clean, about 25 to 30 minutes. Allow muffins to cool in pan for about 2 minutes; remove to a wire rack and cool completely before icing.
Meanwhile, combine icing ingredients in a medium bowl; beat with an electric mixer until creamy, about 1 to 2 minutes. Ice cooled muffins; cover and refrigerate any uneaten muffins. Yields 1 muffin per serving.
Notes
If the mouth-puckering lemon icing isn't enough flavor for you, try adding 1/2 teaspoon each of cinnamon, nutmeg and ginger to the flour mixture.