Place very thinly sliced zucchini and onion in a large mixing bowl and let sit to drain for at least 45 minutes.
Transfer zucchini and onion to a cheesecloth and squeeze extra liquid into the bowl, set veggies aside.
Add the remaining ingredients to the mixing bowl. Stir together until a batter forms.
Add zucchini and onion to bowl, stir to coat, then transfer to a lined baking sheet. Spread into even layer.
Bake at 400F for 40 mins, until the edges are golden. Remove from oven and let cool for 10 mins before slicing.