Heat olive oil in a sauté pan over medium heat. Sauté onion until translucent. Add spices to pan and cook until toasted, around 1 minute. Add ground lamb and cook until no longer pink, breaking up into small pieces with a wooden spoon as you cook. Remove from heat and allow to cool slightly.

Combine butternut squash and lamb mixture in a medium bowl.

Preheat oven to 375 F.

Roll out each sheet of puff pastry. Cut each sheet into 9 even squares. Using a rolling pin, roll out each square slightly.

Scoop 1 heaping tablespoon into the corner of each square. Fold puff pastry over filling, forming a triangle.

Using the tines of a fork, crimp the edges.

Repeat with second sheet of puff pastry.

Brush each bureka with beaten egg. Top with sesame seeds, nigella seeds or poppy seeds if desired.

Bake 18-22 minutes, until golden on top.