1. Preheat oven to 350°F (175°C) and grease a 9x9-inch baking dish.
2. In a large bowl, whisk together flour, oats, sugar, cinnamon, nutmeg, ginger, baking powder, baking soda, and salt.
3. In another bowl, mix together the oil, eggs, vanilla extract, pumpkin puree, and grated zucchini.
4. Add the wet ingredients to the dry ingredients, stirring until just combined.
5. Pour the batter into the prepared baking dish.
6. For the streusel topping, combine flour, brown sugar, cinnamon, and butter in a bowl. Use a fork or your fingers to mix until crumbly. Sprinkle over the batter.
7. Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool before serving.