This streamlined version of classic Greek spanakopita calls for frozen chopped spinach and frozen filo dough, so active prep is at a minimum. You begin by making the filling, sautéeing onion in butter, then adding eggs, Parmesan cheese, bread crumbs, and seasonings. Add the squeezed, defrosted spinach and crumbled feta. Then layer thin sheets of filo dough in a baking dish, remembering to brush each layer with melted butter. The filling goes in a single layer in the middle, under more layers of buttery filo. Bake, cool slightly, and cut into squares or triangles.