Preheat oven to 350 degrees. Line two, 8"x5" loaf pans with parchment paper. It is helpful to secure the paper with binder clips. Set prepared pans aside.
Using a grater, shred zucchini into a fine-mesh sieve. Press into the mesh of the sieve releasing any excess water. Set zucchini aside leaving in the sieve to let any remaining water drain.
In a mixing bowl, combine the mashed bananas, vegetable oil, sugar, eggs and lemon juice. Whisk together well. Add in the pressed, shredded zucchini and whisk to combine. Set aside.
In a separate bowl, combine the flour, cinnamon, baking powder, baking soda and salt. Using a rubber scraper, gradually add the dry ingredients to the wet ingredients until all dry ingredients are incorporated. Do your best to not overmix.
Divide batter into prepared loaf pans.
In a separate bowl, make the crumble topping by combining the flour, brown sugar, cinnamon and softened butter. Use a fork to make mixture crumbly. Sprinkle the crumble topping over the top of each loaf.
Bake at 350 degrees for 45-48 minutes. To test for doneness, insert a toothpick into the center of a loaf. If the toothpick comes out clean and crumb-free the bread is done baking. Color will be golden brown.
Let loaves cool for 10-15 minutes before slicing.