Grease a 15x10x1-inch baking pan; set aside. In a large mixing bowl, beat the 3/4 cup butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, brown sugar, and baking soda. Beat until fluffy. Add eggs and vanilla; beat on low speed until combined. Add flour. Beat until combined.
Stir in zucchini, coconut,and walnuts. Spread zucchini mixture in prepared pan. Bake in a 350°F oven for 25 to 30 minutes or until a toothpick inserted in the middle comes out clean. Cool on a wire wrack. Cut into 15 squares, then diagonally to form 30 triangular-shaped bars.
For icing, in a small mixing bowl stir together the powdered sugar, 1 tablespoon butter, cinnamon, vanilla and enough milk to reach drizzling consistency. Drizzle over cooled bars.