Cut the lamb steaks into bite-sized pieces.
Slice the leek and carrot and chop the garlic and rosemary leaves.
Cut the potatoes into bite-sized chunks.
Heat the oil in a casserole dish and cook the lamb until it changes colour. Remove the pieces to a plate.
Add the leek and cook for 5 minutes, then add the carrot, rosemary and garlic. Stir for a minute or so, then add the potatoes. Sautee for 2-3 minutes, then pour in the stock and cook for 15 minutes or so.
When the potatoes are tender, add the beans and the lamb. Cook for another 5 minutes.
Turn off the heat, and stir in the lemon juice & zest and the mint.