Preheat the oven to 375 and butter a 1-quart baking dish
Cook the zucchini and onion in a small bit of water until soft, then drain well. Use a potato masher to mash them up.
Mix the eggs and milk or cream together in a small bowl.
Stir in the butter and let it melt. Stir in salt, pepper, parsley, green chiles, 1/2 cup of grated cheese and 1/4 cup of the bread crumbs. By now the squash should be cooled a bit so stir in the beaten egg and milk and mix well.
Pour the zucchini mixture into the buttered dish, Mix together the remaining 1/4 cup cheese and 1/4 cup bread crumbs and sprinkle on the top of the casserole.