Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Whisk flax seed and baking powder together in a large bowl; add eggs and beat until smooth. Beat pumpkin, water, honey, salt, vanilla extract, and cinnamon into flax mixture until batter is smooth. Pour batter into prepared baking dish.
Bake in the preheated oven until a toothpick inserted into the center of the bread comes out clean, about 20 minutes.
