Preheat oven to 350°. Spray an 8” square pan with cooking spray.
Add zucchini, lemon juice, sugar, and cinnamon to a frying pan over medium heat. Cook for about 3-4 minutes, until the zucchini just starts to turn opaque, but is still white. Remove from heat to cool.
Whisk flower, baking powder, salt, and cinnamon together in a medium bowl.
Stir sugar, oil, and egg in a large bowl. Stir in milk. Stir dry ingredients into wet and stir until just combined. Pour into prepared pan.
Sprinkled cooled zucchini evenly over the top of the cake batter.
Make the crumb topping: stir together brown sugar, flour, cinnamon, and oil. Sprinkle over zucchini.
Bake for 30-35 minutes until a toothpick comes out clean.