Heat the oil in a large, heavy, lidded pan. Saute the onions and garlic to soften. Reduce the heat, add the beans in their pods and the lemon juice and season with salt and sugar. Stir, and stew gently for 15 minutes stirring occasionally. Add water and half the dill, adjust to a gentle simmer and cook for 1 hour until the pods are very tender. Leave to cool. Pour the lot into a dish with rest of the dill. Serve with the yogurt and hot pita bread. This dish improves with keeping.