Preheat the oven to 350°F and prepare an 8 1/2 x 4 1/2-inch loaf pan with non-stick spray or the butter and flour method.
In a large bowl, mix all the ingredients except the zucchini. You will add that last, along with the apple mixture. The blend will be thick, but once you add the zucchini and apples, the mixture will thin out and be easier to pour into your loaf pan.
Add the zucchini and apple mixture.
After every ingredient is mixed together, pour it into the pan and make the crumble topping.
To make the crumble topping, use a food processor, fork, or your hands (I prefer clean hands). Combine the cold butter, flour, and confectioners' sugar in a bowl. Make sure the butter is broken down and no larger than a pea when you are done.
Top the bread mixture with the crumb topping and cook for 65-75 minutes. The outside of the bread should be dark brown, and when you insert a toothpick, it should come out with a few crumbs on it, but not wet batter. If you notice that the outside is getting too brown before it has finished baking, add a foil tent over the top of the dish for the final 10-15 minutes.
Let the bread slightly cool before cutting and serving.