Heat a large soup pot over medium heat with oil. Add onions and cook for 10 minutes. Add garlic and cook for another 3 minutes.
Add all remaining ingredients to the pot except for tahini. Bring to a simmer and cook for 20-25 minutes until sweet potatoes and green beans are cooked through.
Once soup is done cooking, stir in tahini.
Divide out soup and serve with your favorite toppings and sides. I recommend using toasted bread.