Add in the flour 1/2 a cup at a time. Then add in the baking soda, ground flax seed, and salt. Fold in the shredded zucchini. If your zucchini has a lot of moisture squeeze some out with a clean towel first.
Gluten Free- I have not tried this recipe with gluten free flour. If you were going to attempt it, I recommend trying Bob's Red Mill 1:1 baking flour. I've always had good luck in baking with this flour.
Other Add Ins: Feel free to add nuts or chocolate chips. They would be delicious!