Cut tips off squash and cut each squash into 3 or 4 pieces. Drop squash into a large saucepan with enough boiling water to cover. Return to boil, reduce heat and cook until tender. Drain in colander and mash.
Combine with beaten eggs, 1-cup breadcrumbs, butter, sugar, salt, onion, and pepper. Turn into a 3-quart casserole that has been lightly sprayed with a nonstick spray. Cover with light layer of breadcrumbs. Bake at 350 degrees for 20 to 25 minutes or until lightly browned.