Preheat your oven to 200°C / 180°C fan oven / 395°F.
Dice the sweet potatoes and place them on a baking tray. Spray some one calorie cooking spray over them, and add a sprinkle of salt. Bake until they are soft enough to push a fork through them, about 20 minutes.
Meanwhile, in a large pot, heat some one calorie cooking spray and add finely diced onion and garlic. Saute until the onion is soft and translucent (5 minutes).
Place 3 jarred roasted peppers, and pat them dry with a paper towel. Dice them roughly, and add them to the pot with the onions and garam masala. Leave it to saute until the peppers have warmed up, about 2 minutes.
Then, add coconut milk, vegetable stock and salt. Bring it to a boil, and leave it to cook for a few minutes.
Add the roasted sweet potatoes, and let the soup simmer for about 10 minutes.
Blend the soup smooth using an immersion blender or a regular blender.
Finally, add seasoning to taste and serve.