1. Heat oven to 350°F. Place paper baking cup in each of 12 regular-size muffin cups.
2. In large bowl, stir cake mix, water, 1/2 cup melted butter, the eggs and lemon peel just until dry ingredients are moistened. Divide batter evenly among muffin cups.
3. Bake 18 to 23 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pan to cooling rack. Cool completely, about 30 minutes.
4. In medium bowl, beat powdered sugar, 1/4 cup butter and 1 tablespoon of the lemon juice with electric mixer on low speed until mixed. Add remaining lemon juice, 1 teaspoon at a time, until creamy and smooth. Beat in 1 teaspoon peel. Frost cupcakes with frosting.