Heat the olive oil over medium-high heat in a large pot or Dutch oven. Add the onion, mushrooms, and ¼ teaspoon salt. Cook, stirring frequently, until the onions and mushrooms soften, about 5-8 minutes.
Add the beef, sprinkle with ¼ teaspoon salt, and cook, stirring frequently, until browned.
Add the cumin, chili powder, and garlic powder. Cook for 1 minute.
Add the butternut squash, remaining ¼ teaspoon salt, tomato sauce, and water, stirring to combine. Cover and cook on medium-low for 15-20 minutes, stirring occasionally, until the squash is tender.
Taste and add additional salt if desired. Serve warm with scallion, cilantro, and avocado if desired.