In a medium saucepan, cook the squash in boiling water until soft, approximately 20 minutes. Drain well and mash. Set aside to cool.

In a medium skillet, sauté diced onions in oil until translucent. Add to mashed squash. Add the sugar, thyme, and nutmeg. Whisk in eggs. Stir in bread crumbs. Season with salt and pepper. Set aside.

Preheat oven to 375 degrees Fahrenheit. Line a quarter sheet pan with parchment paper.

On a lightly floured silicone mat or work surface, roll out one piece of dough to a 10- by 15-inch rectangle. Transfer dough to the prepared pan. Gently press the dough into the edges of the pan and trim off excess dough, leaving a 3/4-inch overhang around all edges.

Pour filling into pan and spread out to fill evenly.

Roll out your remaining piece of dough into a 13-inch-long rectangle. Cut into strips to create lattice top. Weave the lattice strips on the top of the pie. Trim any overhanging dough.

Using leaf shape cookie cutters, cut an assortment of leaves from the dough scraps. Brush the egg wash on top of the leaves and position on the pie as desired.

Bake for 50 to 60 minutes, or until the top is golden brown and filling is set. Rotate pie halfway through cooking to achieve even browning. Serve warm.