Heat olive oil in a large nonstick skillet over medium heat. Add onion, bell pepper, and garlic; cover and cook 5 minutes or until tender. Add chili powder and cumin; cook 1 minute, stirring constantly.
Place onion mixture in a 5-quart electric slow cooker. Add butternut squash and next 6 ingredients (through chiles). Cover and cook on low 8 hours or until vegetables are tender and chili is thick. Sprinkle with cheese; serve with lime wedges.