Preheat the oven to 200°C, fan 180°C, gas mark 6. Separate the sausages and place on a baking tray.
In a small bowl, mix together the honey and mustard, then pour it over the sausages.
Cook in the oven for 35 minutes, turning the sausages half way through the cooking time.
Meanwhile, cook the chopped parsnips in a pan of boiling water for 10 minutes, then add the chopped apples and cook for a further 2 minutes, until both are soft.
Drain the parsnipis and apples, then mash with butter and season to taste.
Heat the tub of onion gravy according to pack instructions, and serve with the sausages and mash.