Heat oil in a large frying pan over medium high heat. Add lamb and onion and cook until meat is browned; stir in beans and cook for about 10 minutes, stirring occasionally.
Stir in tomato paste, water, salt, pepper and mint. Reduce heat to low, cover and simmer for about 1 hour or until cooked through and beans are tender. Check halfway through cooking - if there is too much liquid, simmer uncovered for the remaining 30 minutes.