Add the avocado oil to a large saucepan or dutch oven over medium-low heat. Saute the onion and peppers until slightly softened.
Either puree the leftover sweet potato with 2 cups of stock and add to the pan with the remaining 2 cups of stock OR add the sweet potato puree and the stock to the pan.
Add the cumin and turn up the heat so that the soup comes to a simmer.
Simmer until the peppers are tender, about 20 minutes.
Add the lemon juice, fresh thyme and season to taste with salt and pepper.
Serve as is, or blend until smooth – however you prefer!