Pre-heat the oven to 190°C.
Spray a frying pan with low calorie cooking spray and place over a medium heat. Add the onions, carrots, peppers and garlic and cook for 5 minutes until they begin to soften.
Push the onions and peppers to the outside edge of the pan and add the sausages. Cook for 5 minutes until the outsides are browned.
Add the tomatoes, stock cube, balsamic, Henderson's Relish, oregano and sage and mix well. Simmer for 5 minutes.
Add half the sauce from the mixture to the bottom of a roasting dish and spread it out. Lay 3 of the lasagne sheets on top.
Lay the sausages and the rest of the sauce on top. Place the other 3 lasagne sheets on top.
Spread the cream cheese on top of the lasagne sheets. Sprinkle over the mustard powder and the cheese and loosely cover the top with foil.
Place into the oven for 25 minutes. Remove the foil for the last 5 minutes for extra colour on the top. The lasagne will be ready when you can push a knife into it and feel that the pasta is soft and not crunchy.