Heat the oil in a saucepan over low heat; stir in onion and garlic and cook gently until softened, about 5 minutes. Stir in the pepper slices and diced chilli pepper and cook for a further 5 minutes, stirring every now and again. Pour in the stock and remove from the heat.
Puree the soup in a food processor or blender. Return the soup to the saucepan and stir in the passata or sieved tomatoes. Season to taste and serve with a dollop of plain yogurt and fresh basil leaves.
Very easy recipe, I sieved the tomatoes (tinned) and left the peppers chopped small. Makes a lovely chunky soup, and the chilli makes it more interesting. I didn't use the basil or the yoghurt, but it was fine without. - 16 Sep 2012