Heat oven to 325 F/162 C.
Sieve baking powder into the flour to remove any lumps. Add baking soda, salt, ground cinnamon and whisk all the dry ingredients together.
To a large bowl, add white sugar and brown sugar. Mix well. Pour in the oil and stir to combine. Add eggs and whisk thoroughly. Add the dry ingredients to the wet in 3 parts mixing in between. Add grated zucchini and spread out the lemon zest on top. Mix well. The batter will be thick but you’ll be able to mix it together with a wooden spoon.
Grease and flour two loaf pans, 8.5x4.5 or close in size.
Divide the batter evenly between the two pans. Tap the pans on the counter to get rid of any air bubbles. Bake in the heated oven for 40-45 minutes until a toothpick inserted into the middle comes out clean.
Remove from oven and cool pans on a wire rack for 15 minutes. Slide an offset spatula around the sides of the bread and pull in gently. Turn each pan over and tap the bottom, the bread will come out cleanly. Cool completely on the rack.
Wrap and store in the refrigerator for a few days or slice and freeze for longer storage.