i did one once which worked well but was a lot of work for what i ended up with (would be ok if i'd made more to have for another time!)
from memory i just chopped up onion, lots of garlic and capsicum, fried in a little oil with some cumin, coriander and probably some oregano. then added tomatoes and chopped. added some tomato paste and stock powder, probably a pinch of sugar and cooked for ages until it was nice and thick and 'sweet'.
