Slice the leek, carrot and celery.
Heat the oil to a large casserole dish then put the chicken skin-side facing down in it. Scatter the celery, and leek around it.
Cook for about 10 minutes over medium heat, then turn over the chicken, add the rosemary leaves and garlic and brown the other side too for another few minutes. Keep stirring the vegetables. Add the wine and reduce it by half then pour in the chicken stock. Put a lid on, reduce the heat, and simmer cook for 35 minutes. Alternatively put the dish, covered, in a preheated oven, and cook for 30 minutes (oven temperature should be set to about 180°C).
Add the beans and peas, stir them through, then cook for another 8-10 minutes.
Add the lemon zest and some juice and scatter some fresh herbs over it.
Serve warm.