Grate zucchini on the largest holes of a grater into a colander and combine well with salt. Let zucchini drain 30 minutes. Preheat oven to 200°F. Using hands, squeeze as much liquid from zucchini as possible. In a bowl stir together zucchini, onion, egg, bread crumbs, and pepper to taste until combined well.
Lightly brush a 12-inch non-stick skillet with oil and heat over moderately high heat until hot but not smoking. Drop four 1/8-cup measures of zucchini mixture into skillet and with a spatula flatten into 1/4-inch-thick pancakes. Cook pancakes 2 to 3 minutes on each side, or until golden and cooked through, transferring pancakes to an ovenproof plate. Keep pancakes warm in oven while making more pancakes in same manner.