Preheat your oven to 375°F. Toss the cubed butternut squash with olive oil, salt, and pepper. Spread it in a single layer on a baking sheet and roast for 20-25 minutes, or until tender and slightly caramelized. Remove from the oven and set aside.

In a large skillet over medium heat, add the ground beef and cook until browned, breaking it into crumbles with a spatula. Add the diced onion and minced garlic, cooking until the onion is translucent. Stir in the enchilada sauce, and let it simmer for a few minutes to allow the flavors to meld together.

Lightly grease a 9x13-inch baking dish. Begin by layering four tortillas on the bottom of the dish. Spread half of the beef mixture over the tortillas, followed by a layer of roasted butternut squash and a sprinkle of cheese. Repeat the layers with the remaining tortillas, beef mixture, squash, and cheese.

Cover the dish with foil and bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden brown. Let it cool slightly before serving.

Cut the enchilada bake into slices and serve warm. Garnish with fresh cilantro or slices of jalapeño if desired for an extra kick.

Allow any leftovers to cool completely before transferring to an airtight container. Store in the refrigerator for up to 3 days. Reheat in the oven or microwave until warmed through before serving.