Preheat oven to 350°F.
Grease an 8" or 9" round baking pan.
Wash and slice zucchini. Boil zucchini slices with onion, garlic and ½ teaspoon salt in about 1½ cups water until tender.
Drain cooked mixture well and mash.
Beat eggs and add melted butter, milk, breadcrumbs, oregano, ½ teaspoon salt and 1½ cups of the cheese. Bake for 20 minutes.
Top with remaining ½ cup cheese and bake an additional 10 minutes.
Let sit for 5 minutes. Cut into wedges.