Finely chop the carrots and slice the leeks.
Heat the oil in a large casserole dish. Add the leek, carrot garlic and thyme leaves, then gently sauté (under cover) for about 8 minutes until soft, stirring regularly.
Pour in the chicken stock, add the beans and bring to the boil. Cook for about 5 minutes, then add the chicken. Reduce it to a thick sauce for a couple of minutes, then add the lemon zest and juice. Add your chosen greens and cook for 2-3 minutes until wilted or tender.
Serve warm with plenty of ground pepper and crusty bread.