Over medium heat, saute onion in large pot until soft, adding small amounts of water as it sticks. Add ginger, garlic, cumin, coriander, cinnamon and cayenne. Stir to coat onion and cook 1-2 minutes.
To onion mixture add sweet potatoes, carrots, tomatoes and water. Simmer until veggies are soft, 20-30 minutes.
Add garbanzo beans and peanut butter to pot. Using an immersion blender, blend until desired consistency is reached. Or, transfer several cups of soup to a blender, blend until creamy, and add back into the pot and stir.
Season to taste with salt and pepper, and stir in lime juice.