Cook the onion in low fat cooking spray until soft, add the carrots and peppers and cook for 10 minutes.
Add the tomatoes, chilli powder, sugar and stock. Cover and simmer for 15 minutes, cool slightly and blend until almost smooth, season.
Cut the tortillas into short strips. Fry in a frying pan in low fat cooking spray until crisp. (Alternatively you can bake them in low fat cooking spray) set aside on kitchen paper to drain.
Put the avocado, tortillas, cheese and chilli into serving dishes reheat the soup pour into 4 bowls and get people to add their own toppings.