In a pot, heat the oil and add the pumpkin and sweet potato chunks. Let them caramelize properly on at least one side.
Add the garlic and ginger, and fry until fragrant, about 1 minute.
Pour in the water, cover the pot with a lid and bring to a boil. If you like thicker soups, start with less water and add more if needed after blending.
Add the soy sauce, ground coriander seeds, salt, and pepper. Let it simmer on medium heat for 30-35 minutes, until the veggies are very tender.
Stir in the peanut butter, blend the soup, and taste for seasoning. If you want a thinner consistency, add more water now.
Pour in the coconut milk and let it simmer for another 15 minutes.