Preheat oven to 325 degrees. Grease an 8 or 9-inch round cake pan.
In a microwave safe bowl, melt the butter (about one minute). Add the remaining topping ingredients and mix with a fork; set aside.
In a large bowl, whisk together the sugar, oil and eggs. Stir in the zucchini, pineapple and vanilla and mix well.
In a medium bowl, whisk together the baking soda, baking powder, salt, cinnamon, nutmeg, ginger and flour. Stir into the zucchini mixture until just incorporated. Fold in the chocolate chips.
Spread the batter evenly into the prepared pan. Bake for 20 minutes. Remove the pan from the oven and carefully sprinkle with the crumb topping. Return to oven and bake for an additional 20-25 minutes, or until a toothpick inserted in the center comes out clean.
Cool the cake for 10 minutes, then invert (crumb side down) onto a clean plate. Invert again onto a cooling rack to cool for an additional 10-15 minutes.
In a small bowl, combine the powdered sugar and milk until smooth. Drizzle over the cake before serving.