Cut the half head of cabbage in half, cut out and discard the tougher stalk and then finely shred the leaves.
Cut the onion in half, peel it and the cut it into into 3-4mm (⅛") halfmoon shapes.
Heat a 25cm or 10" frying pan over a medium-high heat and when it is hot, add the oil and brown the sausages well on all sides. Remove the sausages and set aside.
Reduce the heat under the pan to medium and then add the onions and soften for 4-5 minutes.
Pour the ham stock into the pan with the onions and add the apple sauce, English mustard, dried thyme, dried rosemary, bay leaf and salt, then give everything a stir to combine.
Add the green lentils, stir to combine with the stock, add a lid and simmer over a low heat for 20 minutes.
Just before the lentils have been cooking for 20 minutes, peel and core the apple, then dice the flesh into a 1cm (just under ½") dice.
Remove the lid from the lentils, add the cabbage and apple, stir to combine and return the lid for 5 minutes. Test for seasoning at this point and add the remaining salt if required.
Return the sausages to the pan, nestling them in with the cabbage and lentils, add a lid then cook for a final 10 minutes, or until the sausages have cooked through.