Thinly slice the leek, garlic and mushrooms. Trim the green beans.
Heat the oil in a large frying pan and gently sauté the leek and garlic for 5 minutes. Add the mushroom and chilli (if used), then sauté for 5 minutes. Add the spices, stir, then add the chipotle paste and tomato purée and stir for a minute.
Add the tomatoes, a drop of water (if it looks dry) and put the lid on. Simmer for about 10 minutes, until the mushrooms have shrank, then add the green beans and more water if needed. Simmer for another 5 minutes, then add some lime juice and chopped coriander leaves.
Season to taste, then serve.