Peel and finely chop the onion. Halve the pepper, scrape out the seeds and white bits then finely chop it. Warm a large pan on a medium heat and add 1 tbsp olive oil. Add the onion and pepper, season with salt and pepper and fry for 7-8 mins, stirring often, till the veg is softened and browned.
While the veg fry, peel the sweet potatoes and chop them into small cubes. Finely chop the rosemary leaves. Peel and grate or crush the garlic. Fill and boil the kettle.
When the onion and pepper have cooked for 7-8 mins, add the garlic and most of the rosemary to the pan and stir for 1 min. Stir the sweet potato into the pan. Pour in 800ml hot water from the kettle. Drop in the sun dried tomatoes. Pop a lid on the pan and simmer for 20 mins.
Meanwhile, place a small frying pan on a medium heat and tip in the pumpkin seeds with a pinch of salt. Toast for 1-2 mins, shaking the pan regularly, till the seeds are darkened and beginning to pop in the pan. Tip the toasted seeds into a bowl.
When the soup has cooked for 20 mins, the sweet potato should be soft when pierced with a sharp knife. Cook a little longer if not.
Blend the soup till smooth using a hand-held blender, or carefully ladle it, in batches, into a blender and blitz. Taste the soup and add more salt or pepper if you think it needs it. Ladle into a couple of warmed bowls and top with the toasted pumpkin seeds and remaining rosemary to serve.