Arrange a rack in the middle of the oven and heat the oven to 400ºF. Line a rimmed baking sheet with parchment paper.
Peel, seed, and dice 1 small butternut squash (about 4 cups). Peel and dice 3 medium sweet potatoes (4 to 5 cups). Place both in a large bowl.
Add the olive oil, salt, black pepper, garlic powder, dried parsley, and dried oregano, and toss to coat. Transfer to the baking sheet and arrange in an even layer.
Bake until the squash and sweet potatoes are golden-brown and tender, 25 to 30 minutes. Meanwhile, make the filling.