First of all, drain your can of beans in a colander and give them a good rinse.
In a deep saucepan, melt your butter over a medium heat and add your onions and peppers (if using).
Sweat the onions until they start to become translucent and start to soften.
Now add your meat to the pan, stir and saute for 15 minutes.
When your meat has browned and started to soften, add your tomato and stir for a few minutes until it starts to break down.
Add your tomato puree, salt and pepper and stir into the mixture.
Now turn the heat to high, pour your water or stock into the pan and stir.
Bring to the boil, cover and reduce to a simmer for 15-20 minutes until the stew is starting to thicken and the lamb has softened.
Now add your haricot beans (kuru fasulye), stir and simmer for a further 10 minutes.
Leave to rest for around 10 minutes and then serve.