Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 4x6-inch loaf pan.
Combine flour, sugar, cinnamon, baking soda, baking powder, and salt in a large bowl.
Whisk pineapple juice, oil, and egg together in a smaller bowl. Pour into the flour mixture and mix together; mixture will be crumbly and dry. Add zucchini and pineapple and mix well until moist, blended, and very thick. Pour into the prepared loaf pan.
Combine oats, coconut, and brown sugar for topping in a third small bowl. Add margarine and toss with a fork until crumbly. Sprinkle over batter in the pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 40 to 60 minutes. Let cool before serving.