Preheat the oven to 200°C/400°F/gas mark 6.
Heat the oil in a large ovenproof casserole dish over a medium heat on the hob. Cook the chicken for about 5 minutes, or until golden brown all over. Remove and place on a plate.
Add the vegetables and sweet potato to the casserole dish and cook until soft, but not coloured. Return the chicken to the casserole with the vegetables.
Make up the gravy by pouring 400ml of boiling water onto the chicken gravy granules and stir well. Stir into the chicken and vegetables. Cover and cook in the preheated oven for 40 minutes, or until the chicken is cooked through.
To make the dumplings, mix the flour, suet, parsley and seasoning, and add enough water to make dough that is elastic, but not too sticky. With floured hands roll the mixture into 8 balls. Then, 25 minutes before the end of cooking, add to the casserole and continue to cook.