Preheat the oven to 375°F (190°C).
In a large skillet, heat the olive oil over medium heat and sauté the onions until translucent, about 5 minutes.
Add the minced garlic and cook for another minute until fragrant.
In a large bowl, combine the cubed butternut squash, sautéed onions and garlic, cooked quinoa, salt, pepper, and heavy cream.
Transfer the mixture into a greased casserole dish and spread it evenly.
Top with shredded cheese and breadcrumbs.
Bake in the preheated oven for 30–35 minutes, until the cheese is melted and the top is golden brown.
Remove from the oven and let it cool for a few minutes before serving.