Spray the casserole pan with low calorie cooking spray and cook the sausages over a medium heat for 7-8 minutes, until well browned. Remove from the pan and set to one side.
Wipe the pan and give it another spray with low calorie cooking spray.
Add the carrots and onions and sauté for 3-4 minutes, over a medium heat.
Add the garlic, sage and mustard powder and stir well.
Add the stock cubes to the water and pour into the pan along with the cider vinegar, then stir in the chopped apple and lentils.
Increase the heat and bring to the boil.
Return the sausages to the pan and reduce the heat to medium-low.
Cover and allow to simmer for 35 minutes, stirring occasionally.
After 35 minutes, the lentils should be tender, and there should be a little stock left. Add a touch more water if desired.
Add the cheese to the pan and stir until it has melted. Taste and season with salt and freshly ground pepper.
Divide between 6 bowls and serve with some pickled beetroot and red cabbage or some crusty bread for mopping up the lentils.