Heat a large skillet over medium heat. Add ground beef, diced onion, minced garlic, salt, black pepper, oregano, and cumin. Break beef into small crumbles with a wooden spoon. Cook 6 to 8 minutes until completely browned with no pink remaining and onions have softened. Drain most fat into a heat-safe container, leaving about 2 tablespoons in the pan. Transfer beef mixture to a plate and set aside.

In the same skillet with reserved fat, add cubed butternut squash. Saute 5 to 7 minutes for frozen and thawed squash, or 12 to 15 minutes for fresh, stirring occasionally, until fork-tender and lightly golden on the edges. Return cooked beef to the pan and stir to combine.

Pour enchilada sauce over the beef and squash mixture. Stir to coat evenly. Bring to a low simmer, then add sliced tortilla strips. Gently fold into the sauce and let soften for 2 to 3 minutes without over-stirring to keep strips intact.

If using cheese, sprinkle over the top and melt for about 1 minute on low heat. Remove from heat. Top with fresh cilantro, chopped green onion, dairy-free sour cream, and sliced avocado. Serve with lime wedges on the side.