Heat oil in a nonstick skillet over medium heat. Add onion and garlic; cover and cook 5 minutes or until tender.
Place onion mixture in a 5-quart electric slow cooker. Add sweet potato and next 10 ingredients (through chiles). Cover and cook on low 8 hours or until vegetables are tender.
Spoon 1 cup cooking liquid into a small bowl. Add peanut butter; stir well with a whisk. Stir peanut butter mixture into stew. Top with peanuts; serve with lime wedges.