Heat oven to 350°F. Grease 12-cup fluted tube cake pan with shortening; lightly flour.
In medium bowl, mix flour, baking powder, baking soda and salt with spoon; set aside.
In large bowl, beat 1 cup butter with electric mixer on medium speed about 2 minutes or until creamy. Beat in 2 cups powdered sugar. Add eggs, one at a time, beating well after each addition. Add flour mixture to butter mixture alternately with milk, beating well on low speed after each addition. Beat on low speed 1 minute. Stir in lemon juice, lemon peel and zucchini. Spoon into pan.
Bake 50 to 60 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes in pan. Remove from pan onto serving plate. Cool completely, about 1 1/2 hours.
In 1-quart saucepan, heat all glaze ingredients just to boiling over medium heat, stirring constantly; remove from heat. Let stand 30 minutes until slightly thickened. Drizzle over cake.