Preheat oven to 180°C.
Heat oil in a large pan and fry the mushrooms until soft.
Add the tinned tomatoes and water then stir in the contents of the sachet of Knorr Naturally Tasty Lasagne Recipe Mix .
Stir in the baby spinach leaves and allow to simmer until they have just wilted then remove the pan from the heat.
In the meantime you can begin to prepare the white sauce – melt the margarine in a pot then stir in the flour to form a roux and allow to cook for 1 - 2 minutes.
Allow to cook then slowly whisk in the milk to form a smooth sauce then reduce heat and allow to cook for 5 – 8 minutes stirring continuously until the sauce has thickened then season to taste.
Using an ovenproof dish begin with a layer of sliced boerewors topped with tomato sauce and then the first layer of lasagne sheets followed by white sauce. Continue building alternating between boerewors, tomato sauce, lasagne sheets and white sauce finishing off with cheddar cheese.
Bake in the oven at 180°C for 35 – 40 minutes.